|SF 593 

T5 H83 
[Copy 1 



U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ENTOMOLOGY— BULLETIN No. 105. 

L. O. HOWARD. Entomoloeist and Chief of Bureau. 



THE ROCKY MOUNTAIN SPOTTED 
FEVER TICK. 

WITH SPECIAL REFERENCE TO THE PROBLEM 

OF ITS CONTROL IN THE BITTER ROOT 

VALLEY IN MONTANA. 



BY 

W. D. HUNTER, 

In Charge of Southern Firld Crop Insect Investigations, 

AND 

F. C. BISHOPP, 

Entomological Assistant. 

tin Cooperation with the Biological Survpy .tikI tlip 
Montana Agricultural College.] 



Issued November 17, 191 1. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1911. 




Qass S^:S43 

Book Tg Hg 3 



r 



U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ENTOMOLOGY— BULLETIN No. 105. 

L. O. HOWARD, Entomologist and Chief of Bureau. ,^L— ^ "^Lm 



THE ROCKY MOUNTAIN SPOTTED 
FEVER TICK. 

WITH SPECIAL REFERENCE TO THE PROBLEM ^.^X 
OF ITS CONTROL IN THE BITTER ROOT fS ^ 

VALLEY IN MONTANA. 



wf^= 






TD.'TIjUNTER, 

In Charge of Southern Field Crop Insect Investigations, 



F. C. BISHOPP, 

Entomological Assistant. 

[In Cooperation with tlie Biological Survey and the 
Montana Agricultural College.] 



Issued November 17, 1911. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1911. 



CxTJ^ 



^ 






^ 



^ 



BUREAU OF ENTOMOLOGY. 

L. O. Howard, Entomologist and Chief of Bureau. 

C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 

R. S. Clifton, Executive Assistant. 

W. F. Tastet, Chief Clerk. 

F. IT. Chittenden, i/i charge of truck crop and stored product insect investigations. 

A. D. Hopkins, in charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal and forage insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. F. Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of moths, field work. 
Rolla p. Currie, in charge of editorial work. 
Mabel Colcord, in charge of library. 

Southern Field Crop Insect Investigations. 

W. D. Hunter, in charge. 

F. C. BiSHOPP, H. P. Wood, W. V. King, G. N. Wolcott, engaged in tick investi- 
gations. 

W. D. Pierce, J. D. Mitchell, E. S. Tucker, T. E. Holloway, G. D. Smith, 
E. A. McGregor, Harry Pinkus, W. A. Thomas, Thomas Lucas, engaged in 
cotton-boll weevil investigations. 

A. C. Morgan, G. A. Runner, S. E. Crumb, engaged in tobacco insect investi- 
gations. 

T. C. Barber, C. E. Hood, engaged in sugar cane and rice insect investigations. 

R. A. Cooley, D. L. Van Dine, Wilmon Newell, A. F. Conradi, C. C. Krumbhaar, 
collaborators. 
2 



i^r nf a 



LETTER OF TRANSMITTAL 



United States Department of Agriculture, 

Bureau or Entomology, 
Washington, D. C, July 20, 1911. 
Sir: I have the honor to transmit herewith a manuscript entitled 
" The Eocl^y Mountain Spotted Fever Tick, with Special Keference 
to the Problem of its Control in the Bitter Root Valley in Montana," 
prepared by Messrs. W. D. Hunter and F. C. Bishopp, of this bureau. 
The work of this bureau on the spotted- fever-tick problem began 
in 1909. It has been conducted in cooperation with the Biological 
Survey of this department and the Montana Agricultural Experiment 
Station. The investigation of the life history and habits of the tick 
which transmits spotted fever has revealed certain feasible and eco- 
nomical methods of control. These methods render it possible to 
reduce the numbers of the ticks to such an extent that the cases of 
spotted fever in the Bitter Root Valley will be very few in number, 
if, indeed, the disease is not eliminated altogether. The plans for 
this work are outlined in this manuscript. 

It is recommended that the accompanying manuscript be published 
as Bulletin No. 105 of this bureau. 

Respectfully, L. O. IIow^\rd, 

Chief of Bureau. 
Hon. James Wilson, 

Secretary of Agriculture. 

3 



CONTENTS. 



Page. 

Introduction 7 

Work upon which this bulletin is based 9 

Possibility of increase of area of spotted fever 11 

Importance of the control of the spotted-fever tick 14 

Summary of facts bearing on importance of tick control 14 

Distribution of the spotted-fever tick 15 

Factors governing abundance 17 

Summary of life history of the spotted -fever tick 19 

The egg and larva 19 

The nymph 19 

The adult 19 

Seasonal history and habits 21 

The host animals of the spotted-fever tick 26 

Other species of ticks found in regions where Rocky Mountain spotted fever 

occurs 31 

Species of ticks which may play an important part in the dissemination of the 

disease should it be introduced into new regions 31 

Practical control or eradication of -the spotted-fever tick 32 

Conditions favoring control 32 

Importance of control throughout the Bitter Root Valley 36 

Methods of destroying ticks 36 

Dipping 37 

Construction of vats 38 

Handwork in the destruction of the spotted-fever tick 41 

Definite recommendations for control or eradication of the spotted-fever 

tick in the Bitter Root Valley 41 

Estimated cost of work 42 

Supplementary means of control 43 

Necessity for expert supervision 44 

Bibliography of the more important writings on the spotted-fever tick 45 

5 



ILLUSTRATIONS. 



PLATES. 

Page. 

Plate I. Ticks and spotted fever in the Bitter Root Valley, Montana. Fig. 1 . — 
View in Lo Lo Canyon, which leads into the Bitter Root Valley, 
showing conditions under which ticks thrive. Fig. 2. — Camp 
laboratory near Florence, Mont., in one of the most heavily in- 
fested localities known 8 

II. The Rocky Mountain spotted-fever tick {Dermacentor venustus). 
Fig. 1. — Adult female unengorged, dorsal view. Fig. 2. — Adult 
male, dorsal view. Fig. 3. — Adult female unengorged, ventral 
view. Fig. 4. — Adult male, ventral view. Fig. 5.— Adult female 

in act of depositing eggs 20 

III. Spotted-fever tick {Dermacentor venustus) and Dermacentor albipictus. 
Fig. 1. — Adult spotted-fever tick which has deposited eggs. Fig. 
2. — Larva of spotted-fever tick. Fig. 3. — Engorged nymph of 
spotted-fever tick. Fig. 4. — Same, ventral view. Fig. 5. — Adult 
male of Dermacentor albipictus. Fig. 6.— Adult female of Derma- 
centor albipictus, unengorged 20 

TEXT FIGURES. 

Fig. 1. Map showing area in which the spotted-fever tick occurs 16 

2. Diagram showing possible seasonal history of spotted-fever tick 27 

3. Dipping vat 38 

6 



THE ROCKY MOUNTAIN SPOTTED-FEVER TICK, WITH SPECIAL 
REFERENCE TO THE PROBLEM OF ITS CONTROL IN THE BITTER 
ROOT VALLEY IN MONTANA. 



INTRODUCTIOlSr. 

For many years a disease of human beings, known as spotted fever, 
has been known to occur in certain localities in the Eockj' Mountain 
region of the United States. In fact the evidence is rather conclu- 
sive that the disease existed before the settlement of the country by 
white men. At any rate old residents of the Bitter Root Valley in 
Montana have informed us that the first white settlers were warned 
bj^ the Indians of the danger of contracting a very serious disease 
if they visited certain localities. From what has been learned in 
recent years it is evident that these dangerous localities are the very 
ones in which spotted fever is now most prevalent. 

The States in which the disease occurs most frecjuently are Mon- 
tana and Idaho. There is no doubt, however, that it occurs in at 
least portions of other States, such as Oregon, Washington, Nevada, 
Utah, Wyoming, and Colorado. 

Definite work on the nature and method of transmission of spotted 
fever was not begun until 1902. In that j^ear Drs. Wilson and 
Chowning announced the theory that the "wood tick ' ' is the natural 
agency through which the malady is transmitted from one human 
being to another. This hypothesis was based upon three observa- 
tions: First, that the majority of cases of spotted fever showed 
histories of tick bites ; second, that the localities in which the disease 
was most frequently contracted were those where ticks were most 
abundant ; and, third, that the season of spotted fever coincided with 
the period when the ticks were most frequently observed. Drs. 
Wilson and Chowning had no facilities for proving their hypothesis 
in a scientific manner, but such proof was soon obtained. Accord- 
ing to the late Dr. H. T. Ricketts ^ the first experiments which re- 
sulted in proof of the transmission of spotted fever by the tick were 
conducted b}^ Drs. McCalla and Brereton, of Boise, Idaho, in 1905. 
In these experiments a tick which was found attached to a spotted- 
fever patient was removed and allowed to bite a healthy person. In 

1 Fourth Biennial Report, Montana State Board of Health, p. 3 06. 



8 THE EOCKY MOUNTAIN SPOTTED FEVER TICK. 

eight days this person developed a typical case of spotted fever. The 
experiment was continued by allowing the same tick to bite a second 
person. In this case again a typical case of spotted fever resulted. 
The results of the important experiments of Drs. McCalla and 
Brereton were not published by them. 

In 1906 Dr. H. T. Ricketts, then connected with the University 
of Chicago, began a series of investigations which must always 
be considered classic. Not being aware of the exj^eriments of Drs. 
McCalla and Brereton, Dr. Ricketts started with the hypothesis of 
Drs. Wilson and Chowning. His first work was devoted to determin- 
ing whether guinea pigs and rabbits are susceptible to the disease 
and consequently suitable for inoculation experiments. The original 
exj)eriments with rabbits were somewhat inconclusive, but it was 
found that the injection of blood from a human being suffering with 
spotted fever invariably brought about the disease in guinea pigs. 
In fact in these animals the disease was found to run a course very 
similar to that in human beings. It was thus determined that guinea 
pigs were suitable subjects for experiments to determine whether 
ticks could transmit the disease. On August 4, 1906, Dr. Ricketts 
announced the results of the first experiment in the tick transmission 
of the disease. A small female tick was placed on a guinea pig which 
had been inoculated with the blood of a patient who died of spotted 
fever. The tick was allowed to feed on this inoculated guinea pig 
for two days. It was then removed and placed in a pill box for 
two days. At the end of that time it was allowed to attach to the 
base of the ear of another guinea pig which had not been inoculated 
with spotted fever. After three and one-half days the temperature of 
this guinea pig rose and remained above normal for more than seven 
days. The pig also showed practically all of the other symptoms of 
spotted fever. In fact, there was no doubt whatever that the guinea 
pig contracted spotted fever from the bite of the single tick. As a 
control on the experiment Dr. Ricketts placed two other guinea pigs 
m the cage occupied by the animal upon which the tick had been 
placed. They remained there for two weeks. These two pigs showed 
no indications whatever of fever. Thus the possibility of infection 
by contact or by feces was eliminated. The only difference between 
the conditions surrounding the pig Avhich contracted fever and those 
surrounding the others was that the former was bitten hyfx fever tick. 

During the following year (1907) Dr. Ricketts succeeded in trans- 
mitting the disease by ticks in a number of additional cases. In one 
experiment he found that the male tick as well as the female is 
capable of transmitting the disease. In other experiments it was 
determined that the larval or nymphal tick may acquire the disease 
and retain it through the molting period, and transmit the infection 
in the following stage to another host. The most interesting experi- 



Bui. 105, Bureau of Entomology, U. S. Dept. of Agricultun 



Plate I. 




Fig. 1.— View in Lo Lo Canyon, which Leads Into the Bitter Root Valley, 
Showing Conditions Under which Ticks Thrive. 




Fig. 2.— Camp Laboratory near Florence, Mont., in one of the most Heavily 
Tick-Infested Regions Known. 



TICKS AND SPOTTED FEVER IN THE BITTER ROOT VALLEY, MONT. 



WORK UPON WHICH BULLETIN IS BASED. 9 

merits, however, were with adult ticks. It was found that when an 
adult becomes infected with the disease, the infection passes through 
the eggs developed in the tick, so that the young of the next genera- 
tion may transmit the disease.^ 

The main points determined by Dr. Ricketts are as follows : 

(1) Guinea pigs and certain other animals, as monkeys, are sus- 
ceptible to spotted fever. 

(2) Larval ticks applied to an infected animal contract the infec- 
tion and are able to transmit it to the following or nymphal stage. 

(3) Nymphal ticks feeding upon infected animals acquire the 
power of transmitting the disease as adults. 

(4) Adult ticks are able to acquire the disease by feeding upon an 
infected animal and to transmit it through the egg stage to the suc- 
ceeding generation. 

(5) Infective ticks are to be found in nature. 

The transmission of disease organisms through the egg stage of 
ticks is known in a number of other instances. It is the case with 
the tick Margaropus annulatus Say, which transmits splenetic fever 
of cattle in the soutJiern portion of the United States. The causative 
organism of splenetic fever has actually been found in the eggs of 
this tick. Dr. Ricketts recently made a tentative announcement of 
the finding of the spotted-fever organism in the eggs of Dermacentor 
venustus Banks. Future investigation will undoubtedly result in 
certainty regarding this point. 

Some of the main points determined by Dr. Ricketts were corrobo- 
rated about the same time by Dr. W. W. King, of the Public Health 
and Marine-Hospital Service, whose results were published in the 
Public Health Reports of July 27, 1906. 

WORK UPON WHICH THIS BULLETIN" IS BASED. 

The work of the Bureau of Entomology on the spotted-fever 
tick began in 1908, when the investigation of the life history and 
habits of the species was undertaken. Plans were made for deter- 
mining the distribution of the tick and for the exhaustive life-his- 
tory investigations necessary in the formulation of plans of con- 
trol. Following the plan for determining the distribution of the 
tick, two men were selected, one to travel through the southern 
Rocky Mountain region and the other through the northern. The 
late Mr. F. C. Pratt made investigations in New Mexico, Arizona, 
southern California, and Colorado. Mr. W. V. King, whose work 
as an agent of the bureau began July 1, 1909, made the investiga- 

iThe Rocky Mountain spotted-fever tick, like a number of other species, exists in four 
distinct stages, namely, egj;, larva, nymph, and adult. The eggs are invariably deposited 
on the ground in large masses. The larvse which emerge from the eggs are minute six- 
legged animals. After- feeding upon a suitable host, they drop to the ground and molt, 
becoming nymphs. In this stage they have eight legs. The nymph waits until it can 
attach to a host, engorges blood, drops, molts its skin, and becomes adult. 
8464°— Bull. 105^11 2 



10 THE EOCKY MOUNTAIN SPOTTED FEVER TICK. 

tions in the northern Rocky Mountain region. He explored Wyo- 
ming, Idaho, portions of Utah, and Oregon and Washington. Prof. 
R. A. Cooley, of the Montana Agricultural College, consented to co- 
operate with the bureau by directing the work of Mr. King and by 
submitting specimens from many localities in Montana. During 
1909, Mr. J. D. Mitchell, of the Bureau of Etomology, visited New 
Mexico, and succeeded in determining the southernmost locality in 
which the fever tick is at present known to occur. 

The life-history work upon the tick was conducted at Dallas, 
Tex., by Messrs. H. P. Wood, G. N. Wolcott, and the junior author. 
This began early in 1909 and has continued without interruption. 

In February, 1910, a conference Avas held in Washington, D. C., 
with Prof. R. A. Cooley and Dr. C. Hart Merriam, then Chief of 
the Biological Survey, for the purpose of formulating definite plans 
for the continuation of the Avork. It was agreed that the determina- 
tion of the range of the tick should be continued by correspondence 
rather than by sending men into the field and that the local aspects 
of the problem in the Bitter Root Valle}^ should be investigated b}" 
placing an agent there. The Bureau of Entomolog}" provided the 
necessary funds and established a laboratory near Florence, Mont. 
(See PL I, fig. 2.) Prof. Cooley agreed to supervise the work in 
Montana, and was appointed a collaborator in the bureau on March 
1, 1910. At the same time Mr. W. V. King was appointed to work 
under the direction of Prof. Cooley in the Bitter Root Valley. This 
plan of cooperation has continued doAvn to the present time. 

The results obtained have been due, to a large extent, to the energy 
and acumen of Prof. Cooley and to the high grade of Mr. King's 
work. But a special word must be said about Mr. King. Unde- 
terred by the possibility of contracting spotted fcA'er, he located on 
an abandoned farm in the most dangerous locality known. In the 
immediate vicinity a number of deaths from spotted fever had oc- 
cift-red within a short time. He remained there throughout the sea- 
son of 1910, subject to the risk of contracting the fcA'cr on his dailv 
trips into the field or from the ticks used in the experiments at the 
camp laboratory. His devotion to the investigation outweighed all 
considerations of personal safety. Great credit must also be given 
Mr. C. Birdse.ye and Mr. A. H. Howell, of the Biological Survey, 
for assuming the risk of residence at the laboratory during a por- 
tion of the season of 1910. Mr. Birdseye continued the investiga- 
tion of the mammals of the valley in 1911. 

In addition to the work in cooperation with the Montana Agri- 
cultural College, in 1910, the bureau undertook to obtain informa- 
tion regarding the exact extent of the area in which the spotted- 
fever tick occurs. By means of a system of circulars and the gen- 
erous cooperation of many physicians and other persons throughout 



POSSIBILITY OF INCREASED AREA OF FEVER. H 

the Rocky Mountain region, a very large amount of information 
■was obtained. In fact the correspondents sent in altogether 1,400 
lots of ticks, 850 of which were of the fever species. These repre- 
sented 225 localities in California, Colorado, Idaho, Montana, 
Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. 

Very many of the ticks received during the course of this work 
were in immature stages. Unfortunately our present knoAvledge of 
ticks is not sufficient to enable us to determine the species to which 
immature forms belong. This necessitates very special care in rear- 
ing to maturity the immature forms received. This work was done 
at Dallas, Tex., and naturally involved a large amount of skilled 
attention. 

The information now in hand regarding the spotted-fever tick was 
greatly increased through the cooperation of the Biological Survey 
of this department. In 1910 two agents of this survey, Messrs. A. H. 
Howell and C. Birdseye, were located at the camp laboratory of the 
Bureau of Entomology near Florence, Mont. These agents were 
engaged in the collection of wild mammals upon which one stage or 
another of the spotted-fever tick occurs. This work resulted in 
showing the relative importance of the different mammals found in 
the Bitter Root Valley and adjacent mountains as carriers of the 
spotted-fever tick. It also revealed many points having a bearing 
on the original source of the disease in nature and on other impor- 
tant matters. The Biological Survey has also studied carefully the 
possibility of the eradication or control of all the wild mammals 
which carry the fever ticks. 

In September, 1910, Prof. H. A. Morgan, director of the Tennessee 
Experiment Station, consented to make a trip to the Bitter Root 
Valley and to advise the forces cooperating regarding the sufficiency 
of the data obtained and the feasibility of plans of eradication based 
thereon. 

Of course the authors have made full use of the available literature 
on the investigations that have been conducted by other persons. 
Most useful have they found the first and second spotted-fever re- 
ports of Dr. H. T. Ricketts, published in the Fourth Biennial Report 
of the State Board of Health of Montana. 

POSSIBILITY OF INCREASE OF AREA OF SPOTTED FEVER. 

The approximate area in which spotted fever occurs has been indi- 
cated in a pi-evious paragraph. Since it has been shown, however, 
that a certain tick {Dermacentor venustus Banks) is the onl}'' known 
agent of transmission of the disease in nature, it follows that 
the possible area in which spotted fever may occur is at least coin- 
cident with the range of the tick, exactly as the possible range of 
jelioAv fever is as extensive as is the area in which the mosquito 



12 THE KOCKY MOUNTAIN SPOTTED FEVER TICK. 

which transmits it is to be found. Extensive work conducted by 
the Bureau of Entomology has shown with considerable accuracy 
the area in which spotted fever may be thus propagated. The map 
(fig. 1, p. IG) shows the area in which the necessary agent for trans- 
mission occurs, and consequently the possible geographical distribu- 
tion of the disease. This map is based upon the examination of 850 
lots of spotted-fever ticks received from 230 localities during the 
seasons of 1909, 1910, and 1911. 

One of the most remarkable features of spotted fever is the fact 
that strains of different degrees of virulence exist in different locali- 
ties. In Idaho the death rate is from 5 to 7 per cent. In the 
Bitter Root Valley in Montana, however, the death rate is about 
70 per cent. One consideration which has caused the Bureau of 
Entomology to concentrate its efforts in the Bitter Root Valley is 
the possibility that the virulent form of the disease, now restricted 
to that valley, may eventually be carried into other regions where 
the presence of the tick would make transmission possible. 

There are several ways by which the virulent strain of the disease 
might be carried out of the Bitter Root Vallej-. It could be taken 
either by ticks or in the blood of human beings. Carriage by ticks 
might occur when these animals are transported on men, horses, or 
cattle. Moreover, tick eggs or other stages of the tick which have 
been shoAvn to contain the disease organism might be transported in 
hay or other commodities. There is also a chance that ticks in various 
stages might be transported on the hides of domestic or wild animals; 

As regards carriage of infection in the blood of human beings, our 
conclusions are largely theoretical. It is not known how long the 
blood of a person who is attacked with spotted fever remains in- 
fective. It is probable, however, that it is infective for some days 
before the height of the fever and for some time thereafter. During 
the period either preceding or following the climax of the disease a 
person might leave the Bitter Root Valley. If in another locality 
he should be bitten by the fever tick and the specimen should escape, 
the establishment of the virulent form of the disease would be accom- 
plished. In certain diseases similar to spotted fever, such as splenetic 
fever of cattle, the organism of the disease remains in the blood 
for many years without causing an acute or noticeable attack. 
Nevertheless, all ticks which feed upon these apparently immune 
animals become infected and can transmit the disease in acute form 
to other animals. Although nothing is known as to the persistency 
of the organism of spotted fever in the blood of persons who have 
ajoparently recovered, there is a possibility that it may remain for 
some months or even years. In this way there is a probability of 



POSSIBILITY OF INCREASED AREA OF FEVER, 13 

considerable extension of the territory in which the virulent form 
of the disease occurs, by migration out of the valley. 

Naturally the chances of spread will increase with the develop- 
ment of the Bitter Root Valley and the growth of shipments of 
cattle or movements of people to other regions. These considera- 
tions are sufficient to justify very energetic means for control where 
the virulent form of the disease now occurs and where, as will be 
shown in this bulletin, the practical eradication of the tick, and, 
consequently, of spotted fever, is entirely feasible. 

It has been shown by experiments conducted in the Institute of 
Infectious Diseases in Chicago that several species of ticks other 
than the form which occurs commonl}^ in the Bitter Eoot Valley 
are capable of transmitting spotted fever. A very hopeful feature 
of the situation, however, is that in the valley there is but one tick 
species which attacks man. Therefore the other species are of no 
practical importance as regards spotted fever. Even among the 
species which feed upon the lower animals there are many thousands 
of specimens of Dermacentoi' venustus to every one of all other 
varieties. Moreover, means of control of this one species, such as 
will be described in this bulletin, will serve greatly to lessen the 
number of the other forms. For these reasons, in formulating plans 
for practical eradication it is necessary to consider only the one 
dominant tick in the valley. 

There is one respect, however, in which the discovery that species 
other than Dermacentor venustu8 can transmit the disease may be 
of importance. The other forms occur over wide areas in the east- 
ern and southern portions of the United States. It is conceivable 
that if the disease were once introduced in the blood of a human 
being or otherwise, the other ticks might propagate it and transmit 
it in regions far outside of the territory in which the fever is now 
known to occur. But the danger on this score is not so great as 
might be thought. In the first place, in no localities in the United 
States are any species of ticks as numerous as is the fever species 
in the Bitter Boot Valley and elsewhere in the Rocky Mountain 
region. Consequently, the occurrence of anything like an epidemic 
of the disease would be impossible. Only occasional or rare cases 
could be expected. In the second place, it can not be foretold 
whether spotted fever would find general conditions suitable for 
propagation in localities outside of the Rocky Mountain region. 
Nevertheless the degree of danger from this source, while perhaps 
slight, emphasizes the importance of eradication of the spotted-fever 
tick in the mountain region and also of the discovery of effective 
means of control for all species of ticks wherever the}^ occur. 



14 THE EOCKY MOUNTAIN SPOTTED FEVEE TICK. 

IMPORTANCE OF THE CONTROL OF THE SPOTTED-FEVER TICIC. 

The most conspicuous loss from spotted fever is in human lives. 
In the Bitter Root Valley it was estimated in 1904 that 200 cases of 
the severe type of the disease had occurred up to that year. A con- 
servative estimate of the mortality there, as has been stated, is 70 
per cent. This means a loss of about 140 lives in this small valley. 
At the present time, with an increase in the population of the valley, 
it is estimated that about 20 cases of the disease occur annually. 
This means a loss of about 15 lives each year and this loss is certain 
to increase as the population of the valley becomes larger. 

In Idaho it was estimated in 1908 by Dr. E. E. Maxey that the 
annual average of cases of spotted fever was 375. Undoubtedly, 
as Dr. Maxey pointed out, this estimate is very conservative. In all 
probability 500 would be a small estimate. The comparatively 
small mortality in Idaho would give a loss of human lives each 
year of about 35. 

Taking into consideration the whole area over which spotted fever 
is more or less prevalent, it is conservative to estimate 750 cases 
each year with probably 75 deaths. 

A great indirect injury the tick does in the Bitter Root Valley is 
in preventing the proper development of a region favored by a rich 
soil and by remarkable climatic advantages. As long as it is 
known that a dangerous disease exists there and that persons who 
farm or go into the country are especially subject to it, the valley 
can not prosper as it should. Relief from the tick would imme- 
diately result in increased land values and larger immigrations into 
the valley. 

In a larger way the possibility of the spread of the virulent form 
of the disease outside of the valley must be considered. This alone 
would warrant a much larger expenditure than is actually required 
for extermination or control in the valley. 

SUMMARY OF FACTS BEARING ON IMPORTANCE OF TICK CONTROL. 

It has been proved beyond peradventure by the investigations of 
Dr. Ricketts and others that spotted fever is transmitted in nature 
only by certain ticks. In the region where the disease now occurs 
it is transmitted to man by a single species of tick. Therefore the 
rational method of eradicating the disease is to attack this tick. In 
this way the proper procedure is exactly analogous to that being fol- 
lowed in the eradication of splenetic fever of cattle from the United 
States, by the eradication of the tick which transmits it. In the case 
of splenetic fever, certain more or less effective means of combating 
the disease itself have been discovered. These are in the form of a 
method of preventive inoculation and the administration of certain 



DISTEIBUTION. 15 

drugs. In spite of this it has been found that the only hope for the 
eradication of the disease, or even for practical control, is in the 
destruction of the ticks. Inasmuch as no means of preventing or 
curing spotted fever are known, the importance of attacking the ticks 
is much greater than in the case of splenetic fever. The situation is 
also analogous to that brought about by malaria and yellow fever, 
which, as is well known, are transmitted by certain mosquitoes. The 
control of these diseases in all parts of the world has practically re- 
solved itself into a warfare against the mosquitoes. 

These considerations seem to make it very evident that the logical 
course to follow in the eradication or control of spotted fever is the 
elimination of the tick. The problem becomes purely an entomologi- 
cal one. Under these circumstances, it is most fortunate that certain 
feasible and economical means of eradication, first outlined in a 
rather general way by Dr. Ricketts, have been placed upon an exact 
and certain basis by the recent investigations of the Bureau of 
Entomology. 

DISTRIBUTION OF THE SPOTTED-FEVER TICK. 

As is shown in the accompanying map (fig. 1) the range of the 
Rocky Mountain spotted-fever tick extends throughout the north- 
ern part of the Rocky Mountain region across the Great Basin to 
the eastern edge of the Cascade Range. The southernmost limit of 
the tick is in the northern edge of New Mexico. Although the dis- 
tribution of the species in Canada has not been determined, there 
is little doubt that it extends over the southern half of British Colum- 
bia and the western portion of Alberta. HoAvever, only one accurate 
record of the occurrence of this species in Canada has been made, 
namely, by Dr. H. G. Dyar, who captured two female specimens 
at Kaslo, British Columbia, in 1903. 

While infestation occurs throughout large portions of Montana, 
Idaho, Washington, Oregon, Xevada, Utah, Wyoming, and Colorado, 
comparatively small areas in New Mexico and California are infested. 
The tick probably occurs throughout the entire Black Hills region in 
South Dakota and Wyoming, although but one collection has been 
made in that region. 

Naturallj^ there is no uniformity in the abundance of the tick 
throughout the territory in which it occurs. 

Our knowledge of the local occurrence of the tick throughout the 
Western States is not sufficiently complete to enable us to make 
definite statements as to areas within the whole infested region in 
which comparatively few ticks are to be found. We do know, how- 
ever, that certain sections of the country which are unfavorable for 
the development of the species are only slightly or not at all infested. 



16 



THE EOCKY MOUNTAIN SPOTTED FEVER TICK. 



During the investigation about 850 lots of tlie fever species have 
been collected. The following is a list of the counties and the num- 








:;M;aNT. 






* . 
I • 
I 
t 



N. DAK 



S. DAK. 



NEB. 



::;V;":\- • • • ' vV:"^ •.^ //I'-COL. KAN. 




! ^. OKL. • 




Fig. 1. — Map showing region in tlie United States in wliich tlie Ilocky Mountain spotted- 
fever ticli occurs. Tlie degree of sliading indicates the relative abundance of the tick 
in different sections. (From Bishopp.) 

ber of localities within tho.se counties Avhere the .species has been 
taken by the bureau : 

NUMBER OF LOCALITIES, BY COUNTIES AND STATES. IN WHICH THE SPOTTED-FEVER 
TICK IS KNOWN TO OCCLTR. 

California. — Modoc County, 3; Lassen Comity, 1. 

Colorado. — Boulder County, 4 ; Clear Creek County. ] ; Eagle County, 1 ; 
Garfield County, 1 ; Gunnison County, 1 ; Jefferson County. 1 ; I.,orimer County. 
3; Mesa County, 2; Pitkin County, 1; Summit County, 1. 

Idaho. — Bannock County, 7; BingLani County, 2; Blaine County, 3; Boise 
County, 1 ; Bonner County, 2 ; Canyon County, 1 ; Cassia County, 2 ; Elmore 
County, 3 ; Fremont County, 6 ; Kootenai County, 2 ; Lemhi County, 2 ; Lincoln 
County, 2 ; Oneida County, 4 ; Shoshone County, 1 ; Washington County, 1 ; 
Twin Falls County, 1, 



DISTEIBUTION. 17 

Montana. — Beaver Head County, 3 ; Broadwater County, 2 ; Carbon County, 
1; Custer County, 1; Flathead County, 4; Gallatin County, 5; Granite County, 
5 ; Lewis and Clark County, 4 ; Lincoln County, 2 ; Madison County, 6 ; 
Meagher County, 3 ; Missoula County, 8 ; Park County, 2 ; Powell County, 3 ; 
Ravalli County, 7 ; Rosebud County, 4 ; Sanders County, 5 ; Silver Bow County, 
1 ; Teton County, 2 ; Yellowstone County, 1. 

Nevada. — Eureka County, 1; Humboldt County, 2; Lander County, 2; Lin- 
coln County, 2 ; Nye County, 3. 

'Neic Mexico. — Rio Arriba County, 1 ; San Miguel County, 1. 

Oregon. — Baker County, 1 ; Crook County, 3 ; Grant County, 1 ; Harney 
County, 3 ; Klamath County, 1 ; Lake County, 1 ; Malheur County, 2 ; Sherman 
County, 1; Umatilla County, 2; Union County, 1. 

Utah. — Boxelder County, 2 ; Cache County, 2 ; Iron County, 1 ; Uinta County, 
1 ; Utah County, 3 ; Wasatch County, 3. 

'Washington. — Asotin County, 2 ; Chelan County, 2 ; Douglas County, 1 ; Grant 
County, 1 ; Kittitas County, 1 ; Spokane County, 3 ; Stevens County, 14 ; Yakima 
County, 3. 

Wyoming. — Albany County, 3; Bighorn County, 6; Carbon County, 3; Fre- 
mont County, 6; Latrona County, 3; Park County, 2; Uinta County, 2; Weston 
County, 1. 

The aboA'e is far from being a complete list of those counties in 
which the spotted-fever tick occurs, yet it gives a definite idea of the 
territory infested. It should be understood that the number of lo- 
calities given for a county does not represent the relative abundance 
of the tick in that county. The table includes only the number of 
localities from which the tick has actually been received. Greater 
population or a larger number of collectors in some counties has 
given more localities than in others, while the actual abundance of 
the tick may be exactly the reverse. Further investigation through- 
out the Eocky Mountain region will undoubtedly show the tick to be 
present in the majority of the counties included in the area shown to 
be infested in figure 1. Dr. E. E. Maxey^ (1908, p. 4) reports that 
the tick has been found to occur in all of the counties of Idaho with 
the exception of Latah. 

As is pointed out in Circular No. 136 of the Bureau of Entomology, 
the fever tick is known to occur at various elevations from slightly 
over 500 feet to nearly 9,000 feet above sea level. The species occurs 
in greatest abundance in the area known as the transition zone. It is 
also commonly found in the Canadian and Upper Sonoran life zones. 

FACTORS INFLUENCING ABUNDANCE. 

The occurrence and abundance of this tick within a given locality 
are dependent, to a large extent, upon the presence of favorable con- 
ditions for development. These conditions are. first, the existence of 
the small mammals which serve as hosts for the immature stages; 
second, the presence of large mammals upon which the adults may 

1 See Bibliography, p. 45. 
8464°— Bull. 105—11 8 



18 THE ROCKY MOUITTAIN SPOTTED FEVER TICK. 

engorge, and, third, the existence of a certain amount of protection 
for the development of the stages when not on hosts. As a rule the 
abundance of ticks is dependent upon the amount of vegetation. 
Lands upon which some fallen timber and undergrow^th occurs are 
usually found to harbor ticks in abundance, provided the hosts^-cer- 
tain small mammals and domestic animals — are also present. In the 
Bitter Root Valley the areas in which more or less heavy second 
groAvth has followed the removal of the original timber have been 
found to be most heavily infested wdth ticks. These areas are locally 
known as " slashings." (See PI. I, fig. 1.) 

It has been determined that the direct rays of the sun during the 
sunnner have a markedly injurious effect upon the early stages of the 
tick. This fact may be utilized to some extent, as will be shown later, 
in the control of the species by clearing the land of timber and under- 
brush. In small experiments it has been found that when the seed 
ticks are exposed to the sun during very hot weather they imme- 
diately crawl down the grass to the surface of the soil to seek pro- 
tection, and in the absence of an abundance of moisture death results 
in a very few days. The exposure of freshly deposited eggs to the 
sun at Dallas, Tex., has been found to cause them to shrivel and dry 
within less than a day's time. 

The relative abundance of rain, especially during the spring 
months, in different years has a marked effect upon the number of 
ticks occurring in a given locality. This factor is of little importance 
in the natural control of the adult stage of the tick, but is a potent 
factor in the destruction of the eggs and immature stages, particularly 
after the latter have become engorged and dropped from the animal. 

Several other natural means of control of minor importance are 
also operating to some extent to keep the species in check. In barn 
lots, chickens have been observed to destroy the females which drop 
to the ground after becoming filled with blood. Some wild birds are 
known to feed upon various species of ticks, and in one instance, at 
least, the}^ have been observed to destroy the engorged females of the 
spotted-fever tick. Certain species of ants are also thought to be im- 
portant enemies of the pest, particularly when the ticks are in the 
immature stages. 

Owing to the fact that the Rocky Mountain spotted-fever tick is 
primarily a northern form, and therefore accustomed to severe cold, 
it is doubtful whether severe winters are of much importance in its 
destruction. This is particularly' true where there is an abundance 
of protection provided by brush and litter on the ground. 



SUMMARY OF LIFE HISTORY. 19 

SUMMARY OF LIFE HISTORY OF THE SPOTTED-FEVER TICK. 

As is the case with nearly all species of ticks, this one passes 
through four distinct stages, namely, the egg, the larva or seed tick, 
the nymph, and the adult, 

THE EGG AND IjARVA, 

The eggs (PL II, fig. 5) are small, ovoid, brownish objects, about 
one thirty-eighth of an inch long. These hatch into minute, light 
brown, active six-legged creatures known as larvae or seed ticks. 
(PL III, fig. 2.) Before further development takes place it is neces- 
sary for these seed ticks to feed upon the blood of some animal. 
They usually attach to small mammals, such as ground squirrels, and 
become filled with blood in from 3 to 8 days. They then drop off "the 
host and find a convenient protected place in which to continue their 
development. Before engorging the seed ticlv measures about one 
thirty-seventh of an inch in length, but during feeding the body is 
considerably distended, so that it measures about one-eighteenth of 
an inch in length by one thirty-first of an inch in width when en- 
gorgement is complete. The color of the larva? when engorged is 
slate-gray. Activitj' is greatly reduced on account of the weight of 
the blood imbibed. 

THE NYMPH. 

After a resting period of from 6 to 21 days the skin is shed from 
the body of the engorged seed tick and an active eight-legged nymph 
appears. The extra pair of legs is gained during the resting stage. 
This character is sufficient to distinguish the nymphs from the pre- 
ceding or larval stage. In this stage it is necessary for the young 
tick again to find a host and fill with blood. This feeding period 
requires from 3 to 9 days. "VVlien engorgement is complete (see PL 
III, figs. 3, 4), the nymphs measure about one-sixth of an inch in 
length, while before engorgement the length is usually about one- 
seventeenth of an inch. The engorged njmiphs are bluish gray in 
color and not very active. 

THE ADULT. 

As in the case of the engorged larva?, the nymphs, after dropping, 
seek a protected place in which to transform, and there become com- 
pletely inactive. This resting stage requires a longer period than 
the preceding. During this lime the sexual organs of the ticks de- 
velop. "\"\lien the skins are shed the ticks appear as mature males 
and females. Shorth^ before the molting of the nymphs the light- 
colored shields on the back of the adult ticks can be seen through 
the thin skins which are soon to be shed. After the mature ticks es- 
cape from the nymphal skins they are rather soft and comparatively 



20 THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 

inactive. They soon become dried out and the external structures 
become thoroughly hardened. The color pattern becomes more pro- 
nounced and activity increases. This is the stage in which the ticks 
are ordinarily observed in the spring months. The males (PL II, 
figs. 2, 4) and females (PL II, figs. 1, 3) are nearly the same size, but 
the former have a hard plate or shield covering the entire back. 
Upon this shield is a somewhat complicated pattern formed by white 
bands or stripes. In the female the shield is much smaller, covering 
only the anterior portion of the body. Almost its entire surface is 
covered with wdiite. The portion of the body of the female behind 
the shield is rather soft and elastic. It is usually somewhat w^rinkled 
and of a dark reddishrbrown color. In this stage, as well as in the 
preceding, the ticks have eight legs, but the white markings on the 
backs of both sexes and the presence of a small genital opening on the 
underside near the " heads " of the ticks serve to distinguish them 
readily from the other stages. Of course the size of the adult ticks is 
considerably greater than that of either of the immature stages. 
Prior to feeding they usually measure about one-sixth of an inch in 
length by one-tenth of an inch in width. 

Before reproduction can begin it is necessary for both the males 
and females to feed upon the blood of some animal. They usually 
attach to the large domestic animals, and after feeding about 4 
days or more the males start in search of mates. Fertilization takes 
place on the host, and in from 8 to 14 days after attachment the 
females, having become filled with blood, drop from the host and 
seek a protected place in which to deposit their eggs. During the 
course of feeding the portion of the body of the female behind the 
shield is greatly distended, so that the specimens now measure about 
one-half inch long by one-third inch wide by one-fourth inch thick. 
On account of the enormous distention of the back part of the 
body of the female, the legs and head are rendered inconspicuous. 
A close examination, however, wall show the white shield on the 
back just behind the "head." When the females are filled with 
blood the back part of the body is usually a bluish-gray color. 
Although the males imbibe a certain amount of blood when attached 
to an animal they never increase greatly in size as do the females. 

The females always drop from the host animal before beginning 
the deposition of eggs. Deposition continues for about 30 days, 
during Avhich time several thousand eggs are deposited. (See PL II, 
fig. 5.) During the process of deposition the female gradually 
shrinks in size. A'N'lien all of the eggs are expelled the tick is much 
shriveled (PL III, fig. 1) and has changed in color to a mottled yel- 
lowish. She dies within a few days after the last eggs are deposited. 

While depositing her eggs the female remains in the same place, 
so that all of the eggs are in one large mass. The eggs hatch into 
seed ticks in from 16 to 51 days and the life cycle is again repeated. 



jl. 105, Buri-au of Entomnlovy, U. S. Dept. of Agriculture. 



Plate II. 




The Rocky Mountain Spotted-Fever Tick (Dermacentor venustusl 

Fifi. 1.— Adult I'eiuale, uueimorRed, dorsal view. FIk- 2.— Adult male, dorsal view. ' Fig. 3.— .\didl 
female, unensor^wl, ventral view. Fig. 4.— .\dult male, ventral view. Fig. •'..— .\diiU leniale 
in act of depositing e.ggs. ({ )ri.ginal. ) 



B'jI. 105, Bureau of Erifc,rcol'.g/, U S, D*pt. li-f Agri«.ulfuf'». 



Pl/ite III, 




The SpottechFever Tick 'Dermacentor vemustus) and Dermacentor albipictus. 

Fig 1. — Afl ults^rttfcd- fever tick whifth ha.«i rlepr^itef] («sfi. Fij?.2, — ^Larva oi ^ji'^tferl-fever tick. 
Fi^. 3- — ErisroTged nymph of spotterl-fffrer tir-k, Kj)?, ♦. — Sam^r. Vfimtral riew. Fijf, 5.— AdnJl 
rnaleof htrmrvnerdtirriiBnpiHwi. Fig. 6. — Aflnlt female f/f /'. iiOnpiHiuf, nT>»rn(?r»Tjf»-'J, (f^r^nal.) 



SEASONAL, HISTOEY AND HABITS. 21 

SEASONAL HISTORY AND HABITS. 

For convenience in tracing the life c^'cle of the Hocky Mountain 
spotted-fever tick we will begin with the appearance of the flat or 
unengorged females and males which appear with the first warm 
days of spring. It shoidd be remembered that these ticks have 
remained dormant throughout the winter months. When they are 
rendered active during the warm spring- days they are immediately 
ready to attach to an animal and engorge. Some of these ticks 
pass the winter in places where they are not readily reached by the 
warmth of the sun. Such specimens become active later than others. 
Emergence from winter quarters is therefore gradual, usually 
exteilding over a period of a few months, beginning about the 1st 
of March. 

The time of the beginning of activity in the spring is also depend- 
ent to a considerable extent upon the relative earliness of the season 
and upon the locality. In lesser altitudes, and at the southern limit 
of the range of the species, activity may begin as early as the middle 
of Februarj'^, while in the Bitter Eoot Valley it is probable that the 
ticks seldom become active in numbers before nearly the middle of 
March. 

After leaving their winter quarters the adult ticks begin crawling 
about and usually ascend brush to await a host. They may crawl 
upon trees or other objects so as to get several feet above the ground. 

In all ticks the anterior legs have well-developed sense organs 
located near their tips. These front legs are used as feelers. When 
the tick is disturbed it immediately begins to wave them in an 
endeavor to catch any passing object. 

Having found a host, the ticks crawl about upon it until a suitable 
place for attachment is found. On cattle they are usually found in 
numbers on the dewlap, between the fore and hind legs, and along 
the belly. On horses they are commonly found between the legs 
and sometimes in the mane. They may, however, attach to any part 
of the host. 

Attachment to the host is accomplished by means of a spiny 
beak, which has an opening in the end through which the blood 
of the animal is drawn. In from 4 to 8 days after attaching the 
males begin searching for mates. In order to fertilize the females 
they crawl beneath them, and after mating usually attach to the 
animal immediateh^ under their mates. When the females have 
become one-half engorged the blood is rapidly imljibed, and com- 
plete engorgement is reached in a very short time, after which they 
loosen their hold and drop to the ground. Table I shows the time 
required for the engorgement of females on different hosts and 
during diffeTent times of the year. 



22 



THE EOCKY MOUNTAIN SPOTTED FEVER TICK. 



Table I. — Time required for engorfjcment of females of Dermacentor venustus 

at Dallas, Tex. 



Adults attached. 


Dates of dropping as 
engorged females. 


Period of 
engorge- 
ment. 


Date. 


Host. 


First. 


Last. 


May 15,1908 
Mar. 19,1910 
Apr. 1,1910 
May 4,1910 
Mar. 29,1911 
May 29,19111 


Ox 


May 23 
Mar. 28 
Apr. 12 
May 12 
Apr. 7 
June 3 


June 1 
Mar. 28 
Apr. 13 
May 17 
Apr. 12 
June 15 


Days. 

8-17 

9 

11-12 
8-13 
9-14 
5-17 


Guinea pig 

Ox 


Ox 

Ox.. . 


Goat 





' The specimens in this lot were fertilized and slightly engorged when applied. 

After the dropping of the females the males usually remain on 
the host for some time. We have found that they crawl about over 
the animal, reattaching in different places and fertilizing a number 
of different females after one infestation of females has become en- 
gorged and dropped from the host. 

Immediately after leaving the host engorged females endeavor to 
find some protected place in which to deposit their eggs. As has 
been stated, deposition ninj begin as soon as the seventh day after 
dropping, and all of the eggs, which usually number about 4,000, 
are deposited within 30 days. During the process of egg laying the 
female gradually shrinlvs in size and death takes place within a few 
days after all of the eggs have been laid. The length of time before 
the beginning of egg laying depends largely upon the temperature. 
During cool w^eather a period of 41 daj^s has been loiown to pass 
after dropping before the first eggs were deposited. 

The development of the seed tick begins within the egg as soon as 
it is deposited. After the embryonic tick has grown for about two 
weeks, a small white spot appears on one side of the egg. The 
appearance of this spot enables one to determine whether the eggs 
will hatch. The time required for incubation is largely dependent 
upon temperature conditions. In the Bitter Root Valley Mr. W. V. 
King has determined that this period ranges from 34 to 51 days, 
the longer period occurring in the early spring months. At Dallas, 
Tex., we have observed eggs to hatch as early as 15 days after they 
were deposited, the longest incubation period observed in that 
locality being 41 days. After the small seed ticks hatch from the 
eggs they usually remain clustered upon the eggshells for a few 
days and then crawl upon any object in their immediate vicinity to 
await a host. In this .stage also the front legs are used as feelers, 
and when an animal comes into contact with the seed ticks, these 
immediately catch hold. Naturally during the larval stage, as well 
as during the adult stage, large numbers of the ticks starve before 
finding a suitable host upon which to engorge. The larvae die 
much sooner from starvation than do the other stages of the tick. 



SEASONAL HISTORY AND HABITS. 



23 



During the summer months we have found that all of the seed ticks 
hatching from a mass of eggs usually die within one month after 
the first eggs hatch. In one instance a period of 117 days elapsed 
between the beginning of hatching of the eggs and the death of the 
last seed tick. This is the greatest longevity which we have observed. 
Table II indicates the variations in the time required for the be- 
ginning of egg laying, incubation of the eggs, and length of time 
required for the starvation of the seed ticks : 



Table II. 



-Time required for beginning of deposition of rgg^^, hdtchlng. and 
starvation of seed ticks of Dermacentor vcnttf<tii-'<. 



' Date 
engorged 

female 
dropped or 
was picked 
from host. 



Date first 
eggs were de- 
posited 



Period 
from drop- 
ping of 
female to 
beginning 

of de- 
position. 



Date hatching 
of eggs began. 



Period 




Period 


from be- 


Date 


from be- 


gin n hi g of 


all seed 


ginning of 


deposition 


ticks 


hatching to 


to begin- 


were 


death of 


ning of 


dead. 


last seed 


hatching. 




tick. 


Days. 




Days. 


18 


Sept. 5 


52 


33 


July 25 


76 


51 


Aug. 1 


30 


32 


July 19 


61 


35 


Aug. 15 


82 


29 


July 30 


60 


51 


Sept. 3 


56 


20 


Aug. 31 


80 


47 


Nov. 3 


117 


16 


Sept. 29 


92 


34 


Aug. 11 


21 


16 


Sept. 30 


51 



Mean 
daily 
tempera- 
ture dur- 
ing in- 
cubation. 



June 
Mar. 
Apr. 
Apr. 
Apr. 
Apr. 
May 
May 
May 
June 
June 



11,1909 
28, 1910 
2,19101 

7,1910 
13.1910 
26,1910 
1,19101 
14,1910 
— 19101 

4,1910 
4, 19101 



July 16,1910 



June 27,1909 
Apr. 7. 1910 
May 13,1910 
Apr. 17,1910 
Apr. 20,1910 
May 2,1910 
May 19,1910 
May 23.1910 

....:do. 

June 13,1910 
June 17,1910 

July 25,1910 



Days. 



July 15,1909 
May 10,1910 
July 3, 1910 
May 19,1910 
May 25,1910 
May 31,1910 
July 9, 1910 
June 12,1910 
July 9. 1910 
June 29,1910 
July 21,1910 

Before 
Aug. 10,1910 



"F. 
91.8 
70.49 



74.6 

71.78 

71.6^ 



79.04 
'84.'37 



84.59 



1 These records were made in the Bitter Root Valley in Montana; all others were made at Dallas, Tex. 



Those larvae which succeed in finding an animal upon which to 
engorge usually attach about the head and ears of the host, be- 
come filled with blood, and drop from the animal between the 
third and eighth days. In nature the larvie feed almost entirely 
upon the small wild mammals, although experimentally they have 
been forced to engorge upon cattle. As has been stated, the larvae 
after becoming engorged drop from the animal, find a protected 
place, shed their skins, and become active eight-legged creatures 
known as nymphs. These njanphs emerge from the quiescent seed- 
tick stage from about the middle of July to the beginning of cold 
weather. Some of those transforming during the summer find 
hosts, become engorged, and drop for molting. A few of these 
probably molt to adults before cold weather begins and hibernation 
takes place in the adult stage. These few individuals are the only 
ones which complete their life cycle in a single season. It should 
be emphasized that these nymphs, as well as the seed ticks, feed 
almost exclusively on small wild mammals. Tables III and IV show 
the length of the engorgement and molting periods of larvae and 
nymphs. 



24 



THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 



Table III. — Time required for molting of seed ticks and nymphs of Dermacen- 

tor venustus. 



Seed ticks di-opped 
engorged. 


Date seed ticks 
molted. 


Period 

from 

dropping 

to 
molting. 


Nymphs dropped 
engorged. 


Date nymphs 
molted. 


Period 

from 
dropping 


Date. 


Number. 


First. 


Last. 


Date. 


Number. 


First. 


Last. 


to 
molting. 


1908. 
Apr. 5 

May 17 

1909. 
Aug. 6 

Sept. 1 

1910. 
July 41 
July 81 
July 221 

1911. 
May 22 


23 

15 

7 

56 

Many. 

Many. 
Many. 

110 


1908. 
Apr. 20 

May 27 

1909. 
Aug. 13 

Sept. 7 

1910. 
July IS 
July 19 
Aug. 8 

1911. 
May 30 


1908. 
Apr. 24 

May 30 

1909. 
Aug. 16 

Sept. 10 

1910. 
July 25 

...do 

Aug. 11 

1911. 
June 2 


Days. 
l"5-19 

10-13 

7-10 

f>- 9 

14-21 
11-17 
17-20 

8-11 


1908. 
Aug. 6 

1909. 
Sept. 15 

Oct. 3 

1910. 
Mar. 23 

Apr. 14 
July 21 
Aug. 1 

Aug. 19 


17 
5 
3 
2 

13 

1 
6 

12 


1908. 
Aug. 20 

1909. 
Aug. 6 

Oct. 21 

1910. 
May 4 

May 24 
Aug. 1 
Aug. 14 

Aug. 31 


1908. 
Aug. 22 

1909. 
Aug. 7 

1910. 
Mar. 22 

May 23 

May 30 
Aug. 1 
Aug. 16 

Sept. 4 


Days. 
14- 16 

21- 22 

18-170 

42- 61 

40- 46 

11 

13- 15 

12- 16 



1 These records were made in the Bitter Root Valley, Mont.; all others were made at Dallas, Tex. 

Table IV. — Time required for engorgement of seed ticks and nymphs of Der- 

macentor venustus. 



Seed ticks applied. 


Date of dropping 
as engorged seed 
ticks. 


Period 
of en- 
gorge- 
ment. 


Nymphs applied. 


Date of dropping 
as engorged 
nymphs. 


Period 
of en- 
gorge- 


Date. 


Host. 


First. 


Last. 


Date. 


Host. 


First. 


Last. 


ment. 


1908. 
Apr. 2 

July 12 

1909. 
July 28 

Aug. 2 
Aug. 27 

1910. 
July 191 

1911. 

May 18 


Ox 


1908. 
Apr. 5 

July 15 

1909. 
Aug. 2 

Aug. 7 
Aug. 29 

1910. 
July 22 

1911. 
May 21 


1908. 
Apr. 10 

July IS 

1909. 
Aug. 4 

Aug. 7 
Sept. 3 

1910. 
July 23 

1911. 
May 24 


Days. 
3-8 

3-0 

5-7 

5 

2-7 

3-4 
3-6 


1908. 
Apr. 1 

1909. 
Aug. 13 

Sept. 10 

1910. 
May 24 
Aug. 13 

Aug. 19 

Aug. 172 


0.V 


1908. 
Apr. 5 

1909. 
Aug. 17 

Sept. 14 

1910. 
Mav 30 
Aug. 18 

Aug. 23 

Aug. 22 


1908. 
Apr. 8 

1909. 
Aug. IS 

Sept. 15 

1910. 
May 30 
Aug. 20 

Aug. 28 

Aug. 27 


Days. 

4-7 


do 

Guinea pig. 

Rabbit 

Guinea pig. 

Ground 
squirrel. 

Guinea pig. 


Guinea pig. 
Rabbit 

Bovine 

Rabbit 

Rabbit 

Ground 
squirrel. 


4-5 

4-5 

6 
5-7 

4-9 

5-9 



1 This record was made by W. V. King in the Bitter Root Valley, Mont. Dropping probably began 
on July 21, or the second day after application. 

2 This record was made iii the Bitter Root Valley, Mont. Records not referred to in footnotes were 
made at Dallas, Tex. 

Those lai*v?o which hatch from egg.s deposited by females Avhich 
do not find hosts until late in the spring become engorged during 
July and August and do not molt to nymphs until shortly before 
winter. It is thus necessary for the nymphs which appear late in 
the summer to pass the winter in that stage. These nymphs appear 
in the spring shortly after the emergence of the adult ticks ; that is, 
shortly after the middle of March. They continue to emerge from 



SEASONAL HISTOKY AND HABITS. 25 

their winter quarters for some time, the hist individuals not securing 
hosts upon which to engorge until early in July. These individuals 
molt to adults during the hitter part of the summer, and the resulting 
adults pass the winter before feeding. 

In contrast to the short length of life as exhibited by the larvae, 
we find the vitality of the nymphs and adults to be remarkably 
great. It has been determined that adults collected on vegetation 
during the spring months may survive for a period of 413 days 
without food. These individuals undoubtedly passed the winter in 
the adult stage, and therefore the total length of life must have been 
approximately one and two-thirds years. However, in nature the 
gveat majority of the ticks with a vitality equal to this lot would 
probabhi- find hosts and become engorged. Unfed nymphs have been 
found to survive a period of more than 300 days. It is thus possible 
for ticks which pass the winter in the nymphal stage to live until 
at least Julj^ 15 of the following year. Under natural conditions 
this longevity is probably even greater. 

The following is a summary of the life cycle of the tick: The 
winter is passed as flat or unengorgecl males and females and as un- 
engorged nymphs. The former are present from about March 15 
to July 15, during which time they find hosts and become engorged. 
It is during this period that the pest attacks man and communicates 
to him the germs of Rocky ^Mountain spotted fever. The eggs de- 
posited by the females which find hosts early in the spring hatch 
into larva?, Avhich may develop into adults b}^ the first or middle of 
September. The offspring of the females which become engorged late 
in the season succeed in developing only as far as the unengorged 
nymphal stage before cold weather begins. The overAvintered 
nymphs begin appearing from their winter quarters during the latter 
pait of March. They are to be found upon small wild mammals from 
that time until about the middle of July, at Avhich time the nymphs 
which have developed from the females engorged during that spring 
are also present. Overv.intered nymphs transform to adults during 
the summer and fall, and the majority of these adults pass the 
winter in the unfed condition. A few of the first nymphs to find 
hosts early in the spring may molt to adults sufficiently early in the 
summer to alhnv the adults to become engorged, deposit eggs, and 
the transformation lo proceed to the unfed nj^nphal stage by the 
approach of cold weather, thus. completing a life cycle in one year. 
However, the individuals which proceed with development beyond 
the unengorged adult stage during the same season must be very 
exceptional. AMien the mean temperature is low during the spring 
and early summer it is almost certain that none of the individuals 
which have passed the winter as unengorged nymphs develop further 
than unengorged adults during that season. 



26 * THE EOCKY MOUNTAIN SPOTTED FEVER TICK. 

It has been observed that even though the adults which transform 
from overwintered nymphs are kept confined with the host animal 
during the summer or fall following their maturity, they show no 
marked desire to feed, usually endeavoring to crawl away and be- 
come quiet. Thus the habit of the adults of attaching to hosts in the 
spring appears to be so well established that they can scarcely be 
induced to attach to a host after midsummer. 

From the foregoing statements it is evident that although a few of 
the ticks may complete their life cycle — that is, the transformation 
from unengorged adults to unengorged adults of the next generation, 
or from unengorged nymphs to unengorged nymphs of the next gen- 
eration — during one season, the majority require two years for this 
cycle. Should overwintered nymphs not find hosts until late in the 
season and thus not become adult until the approach of winter, the 
resulting adults, if unable to find hosts, may survive until the second 
spring following. Ticks which pass the winter in the adult stage 
may survive until the second spring following, then engorge and pro- 
duce offspring which develop to nymphs the second summer, pass the 
winter in the nymphal stage, and complete development to unen- 
gorged adults during the third season. Thus it is apparent that 
under certain conditions three years might be required for the com- 
pletion of the life cycle. This would necessitate the destruction of 
the adult ticks during three successive seasons in order to eradicate 
the species. 

Figure 2 shows several of the ways in which development may 
proceed. 

THE HOST ANIMALS OF THE SPOTTED-FEVER TICK. 

The investigations conducted by Dr. Ricketts indicated that the 
Rocky Mountain spotted fever tick is restricted in regard to its 
host relations. Our investigation has shown that this restriction 
of certain stages of the tick to certain classes of animals is very well 
marked. The examination during three seasons of nearly 800 wild 
Tnammals which are inhabitants of tJie Bitter Root Valley and numer- 
ous ohservations made elsewhere have shown that^ with few excep- 
tions^ only the immature stages of the tick are to he found on this 
class of hosts. On the other hand., the large domestic animals are 
the j>rincipal hosts of the adult ticks, and the immature stages are 
rarely, if ever, found upon them. This restriction of the adult stage 
to the larger mammals, now a firmly fixed habit of the tick, undoubt- 
edly arose from the fact that the adult ticks are so large that they 
can be easily removed by the smaller mammals. As will be pointed 
out in the discussion of remedial measures, this habit of the Rocky 
Mountain spotted-fever tick may be taken advantage of in the con- 
trol or eradication of the species. 



SEASONAL HISTORY AND HABITS. 



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28 THE EOCKY MOUNTAIN SPOTTED FEVEK TICK. 

Among the domestic animals which act as hosts for the adult 
stage of the tick, horses and cattle are of prime importance. A 
number of collections indicates that sheep are frequently attacked, 
but with smaller numbers of ticks. Dogs have also been found to 
harbor this species, but in limited numbers only. Among nearly 
100 collections of ticks made on dogs in the territory in which this 
species occurs only 12 lots of this tick have been obtained. Only 2 
of these 12 lots contained females which were sufficiently engorged 
to deposit eggs. This indicates that the majority of the ticks are 
scratched off by the dogs before becoming fully filled with blood. 
Mules and asses have also been found infested with this species, and 
in two instances collections have been made upon hogs. It is not 
likely that the latter host is of much unportance, particularly when 
the animals are kept confined in pens and thus not exposed to the 
ticks. 

Among the wild animals which act as hosts for the adults, the 
mountain goat harbors by far the greatest number. In addition to 
specimens of the adults, nymphs have also been found upon them. 
The broAvn bear and coyote have been found to be infested with 
considerable numbers of spotted-fever ticks, some of the specimens 
being sufficiently engorged to deposit eggs. The snowshoe rabbit 
and jack rabbit have occasionally been observed to be infested with 
limited numbers of adults, but on neither of these hosts have en- 
gorged specimens been captured. The woodchuck has also been 
found to act as a host for the adult stage. In only one instance, 
however, were specimens taken upon this host, although 51 of the 
animals were examined during the investigation. 

The Columbian ground squirrel is undoubtedly by far the most 
important host of the immature stages of this tick in the Bitter Root 
Valley. In other parts of the Western States, where this species 
of ground squirrel does not occur, related species have been found 
to act as hosts for both of the immature stages of this tick. In 
the Bitter Root Valley G5 per cent of the 311 Columbian ground 
squirrels examined were found to be infested with immature ticks 
of the genus Dermacentor. Owing to the fact that very large num- 
bers of the immature stages of ticks belonging to the genus Derma- 
centor collected in the Bitter Root Valley were reared to adult and 
all found to be the Rocky Mountain spotted-fever tick, we can 
say with practical certaint}^ that this is the only species of this genus 
which occurs on the small mammals in that locality. Second in 
importance as a host of the immature stages of this tick in the Bitter 
Root Valley is the yellow-bellied chipmunk. Thirtj'-seven per cent 
of 131 of these mammals which were examined were found to be in- 
fested with seed ticks and nymphs. The pine squirrel is also of much 
importance, as 29 per cent of the 181 mammals examined were in^ 



HOST ANIMAI.S. 



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THE EOCKY MOUNTAIN SPOTTED FEVEE TICK. 



fested. Among the other mammals which are of considerable impor- 
tance as hosts of the immature stages are the large chipmunk, the 
woodchuck, snowshoe rabbit, roclf squirrel, wood rat, white-footed 
mouse, and meadow mouse. 

Our knowledge of the tick hosts in the valley was greatly increased 
by the cooperation of the Biological Survey of this department. 
Messrs. Howell and Birdseye, of the Survey, were located at the 
camp laboratory and made extensive collections during 1910. This 
Avork was continued in 1911 by Mr. Birdseye. Table V furnishes a 
list of the wild mammal hosts of this tick. It includes all the records 
of the Biological Survey,^ as well as a number made independently by 
Mr. King, of the Bureau of Entomology. The mammals are listed in 
the table according to their relative importance as hosts of the im- 
mature stages. It is especially worthy of note that among the wild 
mammals which act as hosts for the adult stage the mountain goat 
and brown bear are the only ones wdiich were found to have ticks 
upon them which were engorged sufficiently to deposit eggs. 

One hundred specimens of the birds commonly found in the valley 
were examined and found to be free from ticks. 

Table YI. — Host animals on ivhlch Dcrmacentor vcnustus in the adult stage 

has been found. 

ON DOMESTIC ANIMALS AND MAN. 



Common names. 


Scientific names. 


Approxi- 
mate 
number 
of hosts 
exam- 
ined. 


Approximate number of 
ticks collected. 


State of engorgement 


Males. 


Females. 


Total. 


of females. 


Ox 




200 

800 

5 

9 

75 

100 

5 

10 

900 

1 


2,000 

2,500 

9 

14 

22 
IS 

2 
400 
1 


2,000 

2,500 

5 

17 

32 

20 

4 

4 

400 




4,000 

5,000 

14 

31 

54 

38 

4 

6 

800 

1 


Unengorged to fully. 




Equuscaballus 

Equus asinus 

Equus asinusXcabal- 

liis. 
vis airies 


Do. 


Ass 


Do. 


Mule 


Do. 


Sheep 


Unengorged to one- 


Dog 


Canis familiaris 

Capra liircus . . . 


half. 
Unengorged to three- 


Goat 


fourths. 
Unengorged to 


Hog 




slightly. 
Unengorged to one- 


Man 


Homo sapiens 

Felis domesticus 


third. 
Unengorged to one- 


Domestic cat 


fourth . 
Unattached. 



ON WILD ANIMALS. 



Mountain goat. 
Coyote 



Brown bear 

Jackrabbit 

Woodchuck 

Snowshoe rabbit . . 

Wildcat 

Badger 



Oreamnos montanus , 
Canis lestes 



Ursus amerieanus 

Lepussp 

Marmota flavi\'enter , 

Lepus bairdi , 

Ivynx Uinta , 

Taxidea taxus 



3 


l.'-fl 


150 


300 


1 


15 


10 


31 


1 


1 


9 


13 


15 


3 





9 


51 


2 or 3 


2 or 3 


5 


4 


2 


1 


3 


1 


1 





1 


4 


21 





1 



Unengorged to fully. 
Unengorged to 

slightly. 
Slightly "to one-fourth. 
Slightly to one-sixlh. 
Slightly. 
One-seventh engorged. 



1 See United States Department of Agriculture, Biological Survey, Cir. No. 82. 

2 Dead. 



OTHER SPECIES OF TICKS. 31 

OTHER SPECIES OF TICKS FOUND IN REGIONS WHERE ROCKY 
MOUNTAIN SPOTTED FEVER OCCURS. 

Five species of ticks other than Dermacentor venustus have been 
found to occur more or less commonly in the Bitter Root Valley of 
Montana. These are: Dermacentor albipictus Pack. (PI. Ill, figs. 
5, 6), Ixodes angustus Neum., Ixodes texanus Banks, Ixodes hhigi 
Bishopp, and Haemaphy sails leporis-palustris Pack. On account of 
the host relations of these ticks it is impossible for them to play any 
important part in the dissemination of Pocky Mountain spotted 
fever. Dermacentor albipictus has been found to occur on practically 
no other animals than horses, cattle, and mountain goats. It never 
attacks man. Neither one of the three species of Ixodes has been 
found to occur on man, and they ver}^ seldom attack the domestic 
animals, being confined to certain of the small wild mammals. The 
las<t-named species confines its attack exclusively to rabbits with the 
exception of the immature stages, which are occasionally found upon 
birds. 

In parts of Idaho, Oregon, Nevada, and Utah, the rabbit Derma- 
centor {Dermacentor parumapertus marginatus Banks) is found 
quite commonly. Like the other common rabbit tick this species con- 
fines its attack exclusively to that host. 

SPECIES OF TICKS WHICH MIGHT PLAY AN IMPORTANT PART IN 
THE DISSEMINATION OF THE DISEASE SHOULD IT BE INTRO- 
DUCED INTO NEW REGIONS. 

Since it has been shown by Dr. Maver, of the University of 
Chicago, that Rocky Mountain spotted fever may be transmitted by 
several different species of ticks, the importance of limiting the 
disease-infested area to the territory now covered is strongly em- 
phasized. 

A closeh^ related species, namely, Dermacentor occidentalis Neum., 
has been found to occur throughout western California and south- 
western Oregon. At present the range of this species does not over- 
lap that of the Roclry Mountain spotted-fever tick. On account of 
the fact that this species is an important pest of man, should the 
disease become introduced into the territory where it occurs its dis- 
semination would be certain. In the eastern and southern United 
States several species occur which commonh^ attack man. Nearly 
all of these have host relations very similar to that of the Rocky 
Mountain spotted-fever tick, and therefore the disease might readily 
be transmitted from animal to animal and from animal to man 
by any of these species. The following species would probably be 
of principal importance in the Southern and Eastern States: The 
lone-star tick {Amblyomma americanum L.) ; the American dog 
tick {Dermacentor variabilis Say), and the gulf-coast tick {Am- 
hlyomma rmiculatum, Koch). In the extreme southern portions of 



32 THE KOCKY MOUNTAIN SPOTTED FEVER TICK, 

Texas and New Mexico the Caj^enne tick {Amblyomma cajennense 
Fab. ) . is a common pest of man. 

PRACTICAL CONTROL OR ERADICATION OF THE SPOTTED-FEVER 

TICK. 

In 1909 Dr. Ricketts suggested, in a general way, a plan for the 
practical eradication of spotted fever from the Bitter Root Valley 
by a campaign against the ticks. It became evident to Dr. Ricketts 
as the result of his work on spotted fever that the only method of 
controlling the disease was by destroying the natural agency of 
transmission. The work of the Bureau of Entomology in cooperation 
with the Montana Agricultural College and the Biological Survey in 
obtaining exact information about the life history and hosts of the 
tick has served to elaborate upon the suggestions made by Dr. 
Ricketts and to make it possible to lay down definite plans that 
should be followed. 

It has been pointed out in this bulletin that the plan of eradica- 
tion, which is dependent upon a knowledge of the tick, is entirely 
feasible and economical. The question now is whether the loss of 
25 or more human lives per year in the Bitter Root Valley, the 
onus placed upon the development of the valley by the presence 
of spotted fever, and the danger of the spread of the virulent strain 
of spotted fever to other regions are not of sufficient importance to 
justify the small cost that the work will entail. A considerable por- 
tion of this cost would be offset by the improved condition of the 
live stock which would result from the destruction of the ticks as 
well as of certain other parasites. 

CONDITIONS FAVORING CONTROL. 

It will be understood from the discussion of the life history of the 
spotted-fever tick that several facts will assist greatly in an attack 
against it. Among these are the following: 

(1) The vast majority of fever ticks which develop to the adult 
^tage in the Bitter Root Valley do so upon horses and cattle, although 
small numbers develop upon sheep and a very few upon dogs. The 
only other domestic animal of any importance in the Bitter Root 
Valley is the hog. Although no fever ticks have ever been found 
upon hogs in the valley the adult form was taken in considerable 
numbers on that host on one occasion in Wyoming. It is therefore 
evident that under some conditions the hog is to be looked upon as 
an agency for the breeding of the ticks. The danger on this score, 
however, is exceedingly remote on account of the method of manage- 
ment of hogs in the valley. In the first place the number of these 
animals is not large. In the second place they are not allowed to 
roam at large but are confined to pens or small inclosures where the 
chances of their picking up fever ticks are very small. If hogs were 



PRACTICAL CONTROL OR ERADICATION. 33 

allowed to roam into the brushy land on the edges of the valley they 
might assume importance, but as the present plan of keeping them 
confined to areas v/here, for all practical purposes, ticks do not 
occur will undoubtedly be continued in the future, it is considered 
safe to ignore them in a plan of practical eradication. 

(2) Aside from the domestic animals the wild species which have 
been found to carry the tick must be considered. These wild mam- 
mals can be divided for the purposes of this discussion into two 
groups, namelv, those small forms which frequent the floor of the 
valley and extend in some cases to considerable elevations in the 
mountains, and the larger forms, like the bear, deer, elk, and moun- 
tain goat, which are more or less confined to the mountainous walls 
of the valley, but nevertheless sometimes visit the fields below. 

Regarding the small wild mammals found throughout the valley, 
it was ascertained by examination of very large numbers of speci- 
mens that they seldom or never serve as hosts for the adult ticks. 
The immature forms of the fever tick are frequently to be found 
upon these mammals, but the development of the adults is practically 
i-estricted to the larger domestic animals. 

Regarding the larger wild mammals it may be said that their 
numbers are rapidly decreasing. Some of them are practically 
extinct. The mountain goat, which appears more or less frequently 
to carry the adult fever tick, never invades the valley proper. In the 
winter it is to be found upon the lower rocks of the mountain walls, 
but it moves back to higher elevations as the snoAV melts. There- 
fore mountain goats tend rather to remove ticks from the valley 
than to plant them there. Among the other possible hosts, the two 
species of deer are rapidly becoming scarce. Moreover, in our in- 
vestigations no fever ticks have been found attached to deer. The 
bear, among the Avild mammals, is probably the most likely to serve 
as a host for the fever tick. It can not be considered that this mam- 
mal is abundant enough, however, to have any important bearing on 
the situation. The same is true of the coyote. In fact the number of 
ticks that could possibly be reared upon all the larger wild hosts would 
not be sufficient to cause any considerable infestation of the valley. 
These mammals can not be ignored altogether, but it is safe to con- 
sider them as comparatively unimportant. They might be of con- 
siderable importance if the project were to exterminate the fever in 
the valley and surrounding regions absolutely. But the plan here 
proposed is to reduce the cases of spotted fever to a practically neg- 
ligible number^n the valley. This is feasible and can be accom- 
plished at small cost, Avhile total eradication of the fever ticks in 
the mountains is not necessary to relieve the situation. 

Since it has been pointed out that the larger domestic animals — 
horses, cattle, sheep, and dogs — are necessary hosts for the propaga- 



34 THE EOCKY MOUNTAIN SPOTTED FEVEE TICK. 

tion of the fever tick, the problem of control becomes very greatly 
simplified. The immature stages may be allowed to develop on the 
small mammals in the valley so long as the adult stage may be de- 
stroyed upon the domestic animals which are necessary for its 
development. 

Of course the reduction of the number of rodents in the valley, 
especially the Columbian ground squirrel, is advisable. These ani- 
mals are more or less serious agricultural pests. They destroy a 
considerable amount of produce, and the inhabitants of the valley 
are in the habit of waging warfare against them. Undoubtedly the 
damage done is abundantly sufficient to warrant this work. The 
reduction of the rodents should be encouraged both on general eco- 
nomic principles and because they carry the immature stages of the 
spotted-fever tick. This line of work may well supplement the 
main work which must be done with the larger domestic animals, 
and will undoubtedly hasten the removal of the fever tick from the 
valley. 

In one respect work against the rodents is of more than incidental 
value. It was found by Dr. Eicketts that five of these animals, 
namely, the go^Dlier, rock squirrel, woodchuck, chipmunk, and moun- 
tain rat, are susceptible to spotted fever, and may serve as the 
original source of the disease in nature, or, at any rate, furnish a 
reservoir from wdiich is derived the infection of human beings by 
the agency of ticks. The main point, how^ever, is to destroy the tick 
which is necessary for the propagation of the disease, and this can 
be done by directing the principal efforts against the ticks on the 
larger animals which are under the control of man. 

There are several facts, in addition to the practical restriction of 
the adult fever tick to the larger domestic animals, which will serve 
to render a campaign of eradication feasible. One of these is that 
the adult ticks are to be found on domestic animals or elsewhere dur- 
ing only a part of the year. Efforts toward eradication need not 
begin before March 1 and there would be no necessity for their con- 
tinuance far beyond June 15. This is the season when the work can 
be done most easily and with smallest risk to the stock. A line of 
attack extending throughout the year is entirely unnecessary. An- 
other favorable factor is the small number of live stock that would 
have to be treated. This is showm by the table below : 

Table yu.—Xmiiljrr of live stock in Bitter Root ValUy. (U. S'. Census. lUOO.) 



Neat cattle. 

Horses 

Mules 

Sheep 



Ravalli Missoula 
County. County. 



22,461 i 13,084 

6,713 i 4,125 

18 36 

58; 212 4,942 



PRACTICAL CONTEOL OR ERADICATION. 35 

Moreover, in tlie Bitter Root Valley eradication would not sutler 
the drawbacks connected with the ownership of large bodies of land 
by single persons which have attended similar work that has been 
undertaken in other j)arts of the coui\try. The total number of 
farms in Ravalli County, as given in the census of 1900, was 891 ; 
their average size 199.4 acres. In Missoula County the same authority 
gives 615 farms of an average size of 2-11.6 acres. 

An additional advantage will be found in the large proportion of 
farms in the county which are operated by their owners. Very 
little difficulty on account of nonresident ownership is to be expected. 
In Ravalli County 77 per cent of the farms are operated by the 
owners, and in Missoula County 89. 

Aside from the specific factors which would operate to facilitate 
eradication of the spotted fever tick, others of a general nature may 
be mentioned, namely, the small size of the valley and its practical 
inclosure by high mountains, and the public interest in eradication 
which has already arisen. The Bitter Root Valley lies between high 
ranges of mountains over which there is practically no travel. The 
upper end of the valley is also closed by high mountains over which 
a very inconsiderable amount of traffic takes place. The lower end 
is narrowed almost to a gorge. Practically all the traffic into or out 
of the valley goes through this narrov/ opening at the northern end. 
The laj^ of the land gives an isolated region into which infection 
from the outside would be very unlikely to take place. For all 
practical purposes the guarding of the lower end for a portion of 
the year would be sufficient to prevent reinfection in case eradication 
is undertaken. The soil of the Bitter Root Valley has been found 
to be exceedingly fertile and especially adapted to certain profitable 
crops. It is recognized by all intelligent residents that the principal 
obstacle to the rapid development which has already begun is the 
occurrence of spotted fever. There is consequently a firmly em- 
bedded popular opinion that the destin}- of the valley demands the 
eradication of the fever tick. 

We may summarize the more important facts and conditions which 
would facilitate eradication of the fever tick as follows : 

(1) Practical restriction of the adult stage of the tick to the 
larger domestic animals. 

(2) The short season in the spring over which it woidd be neces- 
sary to carr}^ on the principal work of eradication. 

(3) The small number of animals that would have to be treated. 

(4) The small size of the farms. 

(5) The preponderance of resident farm owners. 

(6) The isolation of the valley and the existence of effective 
natural barriers against reinfestation. 

(7) A commendable public opinion in favor of removing an im- 
portant obstacle to development. 



36 THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 

IMPORTANCE OF CONTROL THROUGHOUT THE BITTER ROOT VALLEY. 

For several reasons it is necessary to carry on this plan of eradica- 
tion on both sides of the valley. It is known that the fever is very 
much less prevalent on the east than on the west side. This situation, 
however, is undoubtedly in part due to the heavier population on the 
west side and the greater number of live stock. There is every 
reason to believe that the settlement of the east side, with the in- 
evitable increase in the number of live stock and, consequently, of 
opportunities for the ticks to breed to maturity, would result in an 
increased number of cases of spotted fever. That this is not a re- 
mote danger is shown by the fact that the development of the east 
side has already begim and will undoubtedly continue with rapidity. 
We do not wish to be understood as believing that the comparatively 
unsettled condition of the east side is the only reason for the scarcity 
of ticks. There are undoubtedly others. Among these is the greater 
abundance of rodent hosts for the immature stages of the tick on the 
west side. This is due primarily to the larger amount of protection 
in the brush or " slashir.gs," although the settlement of the land and 
the planting oi crops may have tended, by furnishing food, toward 
the multiplication of the rodents. Soil conditions may also have 
something to do with the difference. 

The main point, however, is that the comparative immunity of the 
east side is not likely to continue. Destroying the ticks on both sides 
Avould cost but little more than on one. It would prevent the rein- 
festation of the west side. If it were not done, it would be necessary 
to establish and to maintain a quarantine against live stock on the 
east side. From every point of view it is wise to conduct a thorough 
work and clear both sides of the valley at the same time. 

METHODS OF DESTROYING TICKS. 

The two methods of eradicating ticks wdiich will be found to be 
adapted to the conditions of the Bitter Root Valley are (1) the 
dipping of live stock in vats provided for the purpose, and (2) the 
hand treatment of such animals as can not convenientl}^ be dipped. 

In the case of the tick {Margaropus annulatus Say) which trans- 
mits splenetic fever of cattle, a third method has been found to be of 
great importance. This is the elimination of the ticks from pastures 
by " starving" them. This is accomplished by keeping the cattle out. 
During the warm portions of the year, at least, only a few months 
time without hosts will result in the death of the cattle ticks. Im- 
portant differences between the life history of the splenetic-fever tick 
and that of the spotted-fever tick make that plan entirely imprac- 
ticable in the case of the latter species. The problem of the splenetic- 
fever tick is not complicated by the existence of different hosts for 
the immature and the adult stages. That tick is absolutely depend- 



METHODS OF DESTROYING TICKS. 37 

ent upon cattle and remains on its host until mature. The spotted 
fever tick, however, drops to the ground twice for the purpose of 
molting and develops through the immature stages upon certain 
rodents and other animals. In the opinion of the Biological Survey 
the extermination of these rodents within reasonable time appears 
to be impracticable because of the necessary expense. The problem 
is even farther complicated by the remarkable ability of the fever 
ticks to live for long periods without hosts. As shown in the dis- 
cussion of the longevity of the stages of the spotted fever tick, a 
period of three years, in which horses and cattle were kept out of the 
pastures, would be required before eradication could be brought about. 
Tl^is long period renders the so-called starvation plan entirely 
impracticable. 

DIPPING. 

Undoubtedly the so-called arsenical dip is the one best adapted 
for use in the Bitter Root Valley. In fact this dip has practically 
displaced all others for the destruction of ticks in various parts of 
the world. Crude oils have been used to a considerable extent in 
some cases. They are more expensive than the arsenical dip and 
dangerous to cattle inider some conditions. Serious losses have fol- 
lowed the use of heavy oils in dry regions or where it has been neces- 
sary to drive the cattle any considerable distance after dipping. 

Another advantage that the arsenical dip. will be found to have 
over crude oil for the work in the Bitter Root Valley is that it will 
not act as a repellent. When cattle are oiled a portion of the oil 
remains in the hair and upon the skin for several days. This will 
prevent ticks from attaching. In the case of the arsenical dip, how- 
ever, there is very little repellent effect. As the object of the work 
is to kill the ticks rather than to keep them from the animals, the 
more that can be caused to attach the better. 

The formula for the arsenical dip is as follows : 

Sodium carbonate (sal soda) pounds__ 24 

Arsenic trioxid (white arsenic) do 8 

Pine tar gallons__ 2 

Water to malie do 500 

The preparation of the arsenical dip is described in Farmers' Bul- 
letin No. 378, Methods of Exterminating the Texas-fever Tick, pre- 
pared by the Bureau of Animal Industry of this department, as 
follows : 

In preparing the dip, a large caldron or galvanized tanii is required for heat- 
ing the water in which to dissolve the chemicals. Thirty or forty gallons of 
water should be placed in the caldron or tank and brought to a boil. The 
sodium carbonate is then added and dissolved by stirring. When this is accom- 
plished, the arsenic is added and dissolved in a similar manner. The fire is 
then drawn and the pine tar added slowly in a thin stream and thoroughly 
mixed with the dip by constant stirring. This strong stock solution is diluted 
to make 500 gallons before using. 



ss 



THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 



The only precautions necessary are to see that live stock are not 
allowed to drink it and to avoid heating the animals either before 
or after dipping. The dip can be used repeatedly until it becomes 





befouled by foreign matter. A reasonable estimate of the cost of 
preparing this dip in the valley is $0.0031 per gallon, or $6.20 for an 
amount sufficient to fill a vat of 2,000 gallons capacity. 



METHODS OF DESTROYING TICKS. 39 

CONSTRUCTION OF VATS. 

The specifications for such vats as will be found best adapted to 
use in Montana are taken from Farmers' Bulletin No. 378, already 
referred to, as follows : 

SPECIFICATIONS AND MATERIALS FOB A DIPPING VAT. 

A vat constructed according to the accompanying plans will bold 2,088 gallons 
when filled to a depth of 5 feet. 

Excavation. — Excavate for the vat, as shown by the drawings [fig. 3], to the 
proper dei)th. Level the bottom of the pit for the sills. After the vat is com- 
pleted fill in ai'ound it, using the surplus natural grade, and slope the surface 
^iway from the vat. Dig the holes required for all posts, etc. 

tarpentcr ivork. — The drawings show the vat constructed according to two 
methods. One method is to make the sides of 4 by 4 inch posts spaced about 3 
feet apart and lined with 2 by 8 inch dressed, sized, and bevel-edged plank, 
using 20-i)enny spikes to fasten them to the posts and braces. All the joints are 
to be calked with oakum, well driven in with a calking iron, and pitched. The 
floor of the vat and the inclines are to be made of 2-inch plank, with joints 
calked : the exit incline to have 2 by 4 inch cleats spiked to the plank flooring. 
The slide should have an angle of about 25° and should be covered with No. 16 
galvanized iron. 

The other method is to build the sides of the vat of 2 by 4 inch posts and 2 
by 4 inch braces spaced about 16 inches on centers. The 2 by 4 inch posts and 
braces are to be lined with I by 8 inch tougued-and-grooved flooring, blind 
nailed at every bearing with 10-penny nails. All the .ioints are to be laid in 
Avhite-lead paste and the boards firmly driven up. 

Lumber. — The lumber used in the construction of the vat must be thoroughly 
dried and seasoned stock, free from large and loose knots, straight grained, and 
free from sap. 

Gutters. — The gutters for the dripping pens should be made of sound stock, 
the bottom plank housed Into the sides and ends, and the ends housed into 
the sides. All the joints are to be laid in white-lead paste and thoroughly 
nailed. Gutters are to have a 3-inch fall in 11 feet. 

Bill of materials for vat and Orainiiig pens. 
Vat : 

Sills, 8 pieces 4 by 4 inches by 10 feet long. 
Posts — 

1 piece 4 by 4 inches by 16 feet long. 
1 piece 4 by 4 inches by 14 feet long. 
6 pieces 4 by 4 inches by 12 feet long. 

5 pieces 4 by 4 inches by 10 feet long. 
Braces — 

1 piece 4 by 4 inches by 16 feet long. 

6 pieces 4 by 4 Inches by 12 feet long. 
1 piece 4 by 4 inches by 10 feet long. 

1 piece 4 by 4 inches by 6 feet long. 
Guards — 

2 pieces 2 by 8 Inches by 18 feet long. 

1 piece 2 by 8 inches by 16 feet long. 

2 pieces 2 by 8 inches by 12 feet long. 
1 piece 2 by 8 inches by 10 feet long. 



40 THE EOCKY MOUNTAIN SPOTTED FEVEE TICK. 

Vat — Continued. 
Sides- 
is pieces 2 by 8 inches by 20 feet long. 
25 pieces 2 by 8 inches by 18 feet long. 
2 pieces 2 by 8 Inches by 16 feet long. 

2 pieces 2 by 6 inches by IS feet long. 
Dressed one side and two edges. 
Edges beveled for calliing. 

Floor — 

3 pieces 2 by 10 inches by 20 feet long. 
2 pieces 2 by 10 inches by 16 feet long. 
1 piece 2 by 10 inches by 14 feet long. 

1 piece 2 by 10 inches by 7 feet long. 

1 piece 2 by 12 inches by 12 feet long. 
Dressed one side and two edges. 
Edges beveled for calking. 

Cleats, 4 i)ieces 2 by 4 inches by 12 feet long. 
Lumber for di'aining pens : 

Mud sills, 10 pieces 4 by 12 inches by 2 feet long (ceilar or cypress). 

Sleepers, 4 pieces 6 by 6 inches by 12 feet long. 

Joists, 13 pieces 2 by 12 inches by 12 feet long. 

Floor, 360 feet b. m. tongue-and-groove flooring | by S inches. 12-foot pieces. 

Cleats, 205 linear feet 1 by 3 inches. 

Gutters — ■ 

Sides, 4 pieces 2 by 12 inches by 11 feet long (dresi^ed ). 

Bottom and ends, 2 pieces 2 by 12 inches by 12 feet (dressed). 

Bottom housed into side and ends. Ends housed into sides. All 
joints calked and white leaded or pitched. 
Posts — 

11 pieces 4 by 4 inches by 7 feet long. 

2 pieces 4 by 4 inches by 8 feet long. 
2 pieces 4 by 4 inches by 9 feet long. 

Rails — 

2 pieces 2 by S inches by 18 feet long. 

5 pieces 2 by 8 inches by 16 feet long. 
18 pieces 2 by 8 inches by 12 feet long. 

Braces, 2 pieces 2 by 4 inches by 10 feet long. 
Gates — 

7 pieces 1 by 6 inches by 12 feet long, 

6 pieces 1 by 6 inches by 10 feet long. 
Hardware for vat and draining pens : 

4 pairs 12-inch heavy T hinges and screws. 

4 wrought-iron hooks and staples. 

1 pair wrought-iron hook hinges, 12-inch, wood screw hooks, and screws. 

50 pounds 20-peuny wire nails. 

15 pounds 10-penny wire nails. 

12 square feet No. 16 galvanized iron. 

The vat described is of the proper depth for cattle and horses. 
For sheep a platform should be provided which will rest on legs long 
enough to bring this platform 4 feet below the surface of the dip. 
This can be easily made so that it can be removed or replaced in a 



METHODS OF DESTROYING TICKS. 41 

few minutes to allow, if necessary, for the alternate dipping of 
cattle and sheep. 

In selecting a site for the construction of the vat the desirability 
of having the ground slope away from it on one side should be kept 
in mind. This allows for the draining of the vat through a pipe 
inserted at its bottom. This drain should lead to a basin, prefer- 
ably on waste land. Care should be exercised to prevent animals 
from drinking from the j)Ool into which the old dip is drained and 
also to prevent the dip from being washed into streams used for 
domestic purposes. 

In order to j)revent the dip from becoming diluted by rains and 
to check evaporation, a roof of boards or canvas over the vat is 
desirable. 

HANDWORK IN THE DESTRUCTION OF THE SPOTTED-FEVER TICK. 

For the most part the use of dipping vats will furnish all facili- 
ties necessary for the eradication of the ticks. However, in certain 
cases, as, for instance, in the narrow valleys running some distance 
into the mountains, the expense of constructing dipping vats for the 
small number of cattle present would be prohibitive. Instead of 
driving these cattle considerable distances to dipping vats, it will be 
found sufficient to treat them thoroughly by hand methods. The 
procedure is simply to apply the arsenical dipping mixture liberally 
by means of rags, mops, or brushes, or by means of spray pumps. 
It may be found advisable in some cases to use oil instead of the 
dip, although the main reliance should be placed upon the use of 
the dip. Oil from Wyoming, w^hich will be found perfectly adapted 
to this use, can be obtained in the Bitter Eoot Valley, when pur- 
chased in large quantities, at a cost of about $1.25 per barrel. 

DEFINITE RECOMMENDATIONS FOR CONTROL OR ERADICATION OF THE 
SPOTTED-FEVER TICK IN THE BITTER ROOT VALLEY. 

The following are the steps that should be followed for the control 
or eradication of the spotted-fever tick in the Bitter Root Valley : 

(1) A campaign of education whereby all the residents of the 
valle}^ will be made thoroughly familiar with the feasibility of the 
plan of eradication and wdth what it will mean in the development 
of the vallcA' . 

(2) The obtaining of legislation to make it possible to dip or oil 
all live stock in the Bitter Root Valle3^ In general, public opinion 
would be sufficient to bring about the treatment of a large majority 
of the animals. In a few cases objections would undoubtedly be 
raised by farmers. Without the treatment of all live stock, the plan 
would necessarily fail. For this reason it is absolutely essential to 



42 THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 

provide such legislation as will make it possible to enforce the treat- 
ment of all the animals. 

"(3) The obtaining of an accurate census of the horses, cattle, 
sheep, mules, and dogs in the valley. 

(4) The construction of 10 or more dipping vats. 

(5) The providing of materials to be used in the dipping mixture. 

(6) The organization of a corps of workers to carry on the 
operations. 

(7) The systematic dipping of the horses, cattle, sheep, and dogs 
of the valley on a definite schedule. The time of beginning and of 
discontinuing this work will depend somewhat upon the seasons, but 
should be about as indicated below. Weekly dippings are necessary, 
because, as pointed out in the discussion of the life history of the 
tick, adults may attach to domestic animals, engorge, and drop to 
the gi'ound in a minimum of eight days : 

March 10. 

March 17. 

March 24. 

March 31, (Vat refilled ou this date.) 

April 7. 

April 14. 

April 21. (Vat refilled ou this date.) 

April 28. 

May 5. 

May 12. 

May 19. (Vat refilled on this date.) 

May 26. 

June 2. 

June 9. 

(8) The treatment by hand of the animals in localities remote 
from vats should be undertaken on this same schedule. 

One season's woi'k would certainly result in a very large reduc- 
tion in the number of fever ticks present in the valley. The second 
season's operations Avould bring about still further reduction in num- 
bers, if not practical eradication. Nevertheless, a third season's 
work is required to make certain of the results. 

ESTIMATED EXPENSES OF PRACTICAL ERADICATION OF SPOTTED-FEVER TICK 
IN THE BITTER ROOT VALLEY, MONT., NOT INCLUDING THE COST OF 
EXPERT SUPERVISION AND NECESSARY INVESTIGATION. 

The approximate cost of the work for the three seasons is indi- 
cated in the statement given herewith, which does not, however, 
include the cost of such expert supervision and additionar investiga- 
tion as are required. 



METHODS OF DESTROYING TICKS. 43 

First year: 

10 vats, costing $200 each $2,000 

Each vat to Iia\-e a capacity of 2,000 gallons. 
Cost of filling vats four times during season, at $0.0031 per gallon.*. 248 

Salary of one superintendent, 12 months 1, 800 

Salaries of 10 assistants for 5 months, at $80 each 4, 000 

The period to be covered by these men extends from Feb. 15 to 
July 15. 
Incidentals-- 1,000 

Total, first year 9,048 

Second year : 

'Repairs to vats 200 

Cost of filling vats four times during season 248 

Salary of one superintendent 1, 800 

Salaries of 10 assistants 4.000 

Incidentals 1, 000 

Total, second year 7, 248 

Third year : 

Repairs to vats 300 

Cost of filling vats four times 248 

Salary of one superintendent 1. 800 

Salaries of 10 assistants 4.000 

Incidentals 1,000 

Total, third year 7,348 

Grand total 23, 692 

It may be found that more than 10 vats will be required. In that 
case the output for materials would be increased somewhat. 

After three seasons' operations a very small annual expenditure 
will be necessary to avoid reinfestation of the valley by the incom- 
ing of cattle from other places. This could be easily accomplished 
by employing an inspector at a salary of, say, $100 per month for 
six months' service each year. 

SUPPLEMENTARY MEANS OF CONTROL. 

The main reliance in work of controlling the spotted-fever tick 
must be placed upon the dipping and hand treatment of domestic 
animals. However, there are certain supplementary means of con- 
trol which should be practiced. These are (1) the reduction in the 
number of rodents in the valley and (2) the clearing of the brush 
land along the edges of the valley. 

As has been explained in this bulletin, the destruction of the ro- 
dents is not a vital part of the plan of eradication we propose. 

^The cost of dip per gallon is computed as follows: Arsenate trioxide, 5i cents per 
pound; sodium carbonate, 2 cents per pound ; tar, 33J cents per gallon. 



44 THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 

Nevertheless, if the number of these animals can be reduced, it will 
have an important effect in lessening the number of ticks present. 
In addition to this reason for control, the rodents are pests of con- 
siderable importance. Their extermination from the valley, if pos- 
sible, would amply repay the residents in the preventing of losses 
to their crops. 

The conditions existing in the brushy land or " slashings " along 
the edge of the valley are especiall}^ favorable to the tick. Not onh^ 
is shade and protection furnished, but the presence of the timber 
furnishes the rodent hosts favorable opportunities for multiplication. 
In this way the presence of the brush has an important bearing upon 
the abundance of ticks. If the land should be cleared, the ticks 
would be considerably affected. Clearing the lands will, of course, 
increase their value and make possible their planting in orchards or 
other crops without loss of time when the fever tick shall have come 
under subjection. 

For a full list of the mammals found in and around the valley and 
for methods for their extermination the reader is referred to Circu- 
lar 82 of the Biological Survey of this department. 

It is not considered necessary to have these supplementary means 
of control supported by funds raised for the main operations. The 
work of destroying rodents and of clearing the brush lands should 
be conducted by residents on their OAvn initiative. The matter 
should be sufficiently explained and the residents should by every 
means possible be encouraged to undertake the worlv. 

NECESSITY FOR EXPERT SUPERVISION. 

In the work of controlling the spotted-fever tick in the Bitter 
Root Valley it is absolutely essential that expert entomological 
supervision be provided. Since the whole campaign depends upon 
a knowledge of the habits and life history of ticks it must be evident 
that the work must be in the hands of persons who are thoroughly 
familiar with the subject. Among the many reasons why this expert 
supervision is necessary are — 

(1) The proper time to begin and to discontinue the dipping or 
oiling must be determined. This will depend upon the seasons and 
the time when the tick begins to develop in the spring. Unless men 
are at hand to determine when to begin and when to end, much un- 
necessary work might be done or, what is worse, man}^ ticks might 
escape. 

(2) It is necessary to be certain that the dipping solution is kept 
up to a strength sufficient to kill and to see that the dipping is prop- 
erl}^ done. The test of the strength of the solution should be con- 
ducted by experiments the results of which could be interpreted 
safely only by experts. 



BIBLIOGRAPHY. 45 

(3) The campaign of education which should be conducted in con- 
nection with the other work can only be carried on effectively by 
persons who by training and experience know thoroughly the points 
upon which the system is based. The best work can only be done by 
those who have had experience in similar problems and who are 
familiar with data sufficient to refute such fallacious arguments as 
may be adduced from time to time. 

(4) It is possible that means of control additional to those enu- 
merated in this bulletin may be discovered. The chance of such 
discoveries and the consequent hastening of the work will be in- 
creased if persons trained in entomological work are in charge. 

BIBLIOGRAPHY OF THE MORE IMPORTANT WRITINGS ON THE 

SPOTTED-FEVER TICK. 
1908. Anderson, J. F. 

Spotted fever (tick fever) of the Rocky Mountains. A new disease. 
<BuI. 14, Hygienic Laboratory, U. S. Public Healtli and Marine- 
Hospital Service, pp. 50, pis. 1-3. 

1905. Stiles, Cii. Wardell. 

A zoological investigation into the cause, transmission, and source of 
Rocky Mountain '' spotted fever." <Bul. 20, Hygienic Laboratory, 
U. S. Public Health and Marine- Hospital Service, pp. 121. 
A valuable bibliography is included. 

1906. RiCKETTS, H. T. 

The study of " Rocky Mountain spotted fever" (tick fever?) by means 
of animal inoculations. A preliminary communication. < Journ. Amer. 
Med. Assn., vol. 47, no. 1, pp. 33-30. 
1906. King, W. W. 

Experimental transmission of Rocky Mountain spotted fever by means 
of the tick. Preliminary note. <Public Health Reports, U. S. Public 
Health and Marine-Hospital Service, vol. 21, no. 30, pp. 863-S64, 
July 27. 
1906. RiCKETTS, H. T. 

The transmission of Rocky Mountain spotted fever by the bite of the 
wood tick {Dermacentor occidentalis) . < Journ. Amer. Med. Assn., 
vol. 47, no. 5, p. 358, August 4. 

1906. RiCKETTS, H. T. 

Further observations on Rocky Mountain spotted fever and Derma- 
centor occidentalis. <Journ. Amer. Med. Assn., vol, 47, no. 14, pp. 
1067-1069, October 6. 

1907. RiCKETTS, H. T. 

Observations on the virus and means of transmission of Rocky Moun- 
tain spotted fever. <Journ. Infectious Diseases, vol. 4, no. 1, pp. 
141-153. 
1907. RiCKETTS, H. T. 

The role of the wood tick (Dermacentor occidentalis) in Rocky Moun- 
tain spotted fever and the susceptibility of local animals to this dis- 
ease. A preliminary report. <Journ. Amer. INIed. Assn., vol. 49, pp. 
24-27. 
1907. RiCKETTS, H. T. 

Further experiments with the wood tick in relation to Rocky Mountain 
spotted fever. <Journ. Amer. Med. Assn., vol. 49, pp. 1278-1281. 



46 THE ROCKY MOUNTAIN SPOTTED FEVER TICK. 

190S. Maxey, E. E. 

Rocky Mountain spotted (tick) fever witli special reference to casual 
factors, mortality, and geographical distribution in Idaho. <Me!flical 
Sentinel, Portland, Oreg., December. 
1908. Stewart, J. L., and W. F. Smith. 

Clinical phases of Rocky Mountain spotted fever. <Medical Sentinel, 
Portland, Oreg., December. 

1908. RiCKETTS, H. T. 

Recent studies of Rocky Mountain spotted fever in Montana and Idaho. 
< Medical Sentinel, Portland, Oreg., December. 
1908. TuTTLE, T. D. 

Some indications for State control of Rocky Mountain tick fever. 
<Medical Sentinel, Portland, Oreg., December. 

The four preceding papers were republished by the Medical Sentinel with con- 
tinuous pagination under the title " Symposium on Rocky Mountain Tick Fever." 

1908. Banks, Nathan. 

A revision of the Ixodoidea or ticks of the United States. <Tech. 
Ser. 15, Bur. Ent., U. S. Dept. Agr., pp. 1-61. pis. 1-10. 

1908. Smith, W. F. (See Stewart, J. L.) 

1909. RiCKETTS, H. T. 

A microorganism which apparently has a specific relationship to Rocky 
Mountain spotted fever. A preliminary report. <Journ. Amer. Med. 
Assn., vol. 52, no. 5, pp. 379-380. 
1909. RiCKETTS, H. T. 

Spotted Fever Report No. 1, General report of an investigation of 
Rocky JNIouutain spotted fever, carried on during 1906-7. <4th Bien. 
Rept. State Board Health Montana, pp. 87-130. 
1909. RiCKETTS, H. T. 

Spotted Fever Report No. 2. A report of investigations carried on 
during the winter of 1907-8 and the spring and summer of 1908. 
<4th Bien. Rept. State Board Health Montana, pp. 131-191. 

The two papers above constitute the most detailed and comprehensive of 
Dr. Ricketts's various reports on his investigations in Montana. 

1909. CooLEY, R. A. 

Preliminary report on the wood tick. <6th Ann. Rept. Mont. Agr. Exp. 
Sta., pp. 95-104, 1 plate, 1 fig. 

This paper was also published as Bulletin 75 of the Montana Agricultural 
Experiment Station, together with the following : 

1909. CooLEY, R. A. 

Account of trip into West Gallatin Canyon to study ticks. <Bul. 75, 
Mont. Agr. Exp. Sta., pp. 105-108. 

1910. Stiles, Ch. Wardell. 

The taxonomic value of the microscopic structure of the stigmal plates 
in the tick genus Dermacentor. <Bul. 62, Hygienic Laboratory, 
U. S. Public Health and Marine-Hospital Service, pp. 72, pis. 43. 

1911. BiSHOPP, F. C. 

The distribution of the Rocky Mountain spotted-fever tick. <Cir. 136, 
Bur. Ent., U. S. Dept. Agr., pp. 1-4, 1 fig. 

1911. TUTTLE, T. D. 

Rocky Mountain spotted (tick) fever. <5th Bien. Rept. State Board 
Health Montana, pp. 9-12. 
1911. JNIaver, Maria B. 

Transmission of spotted fever by other than Montana and Idaho ticks. 
<Journ. Infectious Diseases, vol. 8, no. 3, pp. 322-326. 



BIBLIOGRAPHY. ■ 47 

1911. Mavee, Maria B. 

Trausmlssion of spotted fever by the tick in nature. <.Joiira. lufec- 
tioiis Diseases, vol. 8, no. 3, pp. 327-329. 
1911. Moore, Josiaii J. 

Time relationsliips of the wood-tick in the transmission of Rocliy 
Mountain spotted fever. <Journ. Infectious Diseases, vol. 8, no. 3, 
pp. 339-347. 
1911. COOLEY, R. A. 

Tick control in i-elation to the Rocky Mountain spotted fever. A 
report of cooperative investigations conducted by the Bureau of 
Entomology and the Montana Experiment Station. <Bul. 85, Mont. 
Agr. Exp. Sta., pp. 1-29. 
1911. Hunter, W. D., and Bishopp, F. C. 

Some of the more important ticks of the United States. < Yearbook, 
U. S. Dept. Agr. for 1910, pp. 219-2.30, 2 pis. 
1911. Henshaw, Henry W., and Birdseye, Clarence. 

The Mammals of Bitter Root Valley, Montana, in their relation to 
spotted fever. <Cir. 82, Bur. Biol. Survey, U. S. Dept. Agr., pp. 1-24, 
12 figs. 

The important papers of Dr. Ricketts have recently (May, 1911) 
been reprinted by the University of Chicago Press in a memorial 
volume entitled " Contributions to Medical Science." 

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LIBRARY OF CONGRESS 



